Okay, okay, I know his thread is 11 years old now, but I came across it and I thought I would try to answer the OP's original question. It was fun to think about, and I'm a huge fan of the PS2 Bounty Hunter game.
A lot of people made some really good points in this thread, and I really enjoyed reading what the rest of you wrote. For starters I think Montross is a fascinating character. He is presented a dark reflection of Jango, who is himself technically a villain, even though the Bounty Hunter game presents him in a more sympathetic light. Montross is far more ruthless by comparison, and he's a way bigger dick than Jango is.
Would Montross have beaten Jango?
I think the answer to this has to be a resounding yes. Throughout the game Montross is shown to become increasingly more challenging, aggressive, and harder to beat, implying that for the earlier matches in the story he was merely holding back or toying with Jango. Furthermore, even if the player manages to make it all the way to the final confrontation with Montross without ever dying once, almost everyone who faces Montross on Kohlma on their first play-through certainly dies, and the developers were so confident about this happening that they gave a special ending with Montross standing over Jango's dead body.
There is a great point made earlier in this thread that Montross largely rode on Jango's coat-tails throughout the majority of the story in the hunt for Komari Vosa, so naturally there is a logical question as to Montross's resourcefulness. Jango does appear to be overall more resourceful than Montross. Despite the fact that Montross got to Groff Hogg (the drug smuggler on Corusant) before Jango did, and that Montross somehow got all the way through Sebolto's death stick factory before Jango, it is heavily implied that Jango is "leading" the hunt and Montross is merely "shadowing" him, as Vosa says to her Bando Gora captain. In fact, after a certain point in the game, Vosa knows of Jango Fett by name, but Montross is simply "the one who shadows him."
On the other hand, one can also make the case that it was smarter for Montross to let Jango (who Montross always saw as a grunt) do the majority of the "work" needed to find Vosa. This explains why Montross was content to let Jango track Vosa through Tatooine while he simply went to Rozatta's station, knowing that if Jango found the information he would certainly inform Roz. Montross has been shown to be something of a thrill-seeker (he explicitly says that he is driven solely by the thrill of the hunt, not by the money), and killing the Longo Two-Gun gang would undoubtedly have been thrilling for Montross, so it is possible that he would have gone through Tatooine himself if he had killed Jango earlier. It does make sense, however, that he is more interested in the hunt for Vosa than getting caught up in a gang war involving the Hutts. Why risk getting killed unnecessarily on Tatooine either by the gang or by Gardulla's krayt dragon and lose out on the ultimate hunt in Vosa? Again, this is not to suggest that Montross was "afraid" of Tatooine, but it was just easier to do it his way when Jango was already going there. Plus, given the implication in the cutscenes that Montross felt somewhat humiliated after his battle with Jango on Malastare, roughing up Roz at her station was a way to stick it to Jango.
It does seem at least somewhat that Jango is a vastly better fighter than Montross, based on the early fights, but again, one can make the case that Montross was holding back and didn't really get serious until the final fight on the moon of Bogden. First, compared to Jango, Montross is severely handicapped by the fact that he's not wearing a full set of Mandalorian armor or using the full arsenal of Mandalorian weapons as Jango is. In the first fight, Jango has a jetpack, saber darts, a flamethrower, and his whipcord, while all Montross has is his two guns - which, if you watch him fight, he does seem to fight almost passively with Jango, barely shooting at him at all. This appears to be entirely by design, i.e. Montross is choosing not to fight Jango that seriously. Furthermore, the first fight concludes when Montross says, "I don't have time for games," and he voluntarily exits. So how much of this was just a spar for Montross?
In the second fight, Montross appears to be employing a vastly different strategy with Jango. At the loading dock at Sebolto's death stick factory, Montross is riding on a skiff and shooting rockets at Jango. Based on Montross's dialogue, it does sound like Montross is taking this fight a little more seriously. He vows to take Jango's new ship (Slave I), for instance. His strategy here seems to be to keep his distance from Jango so the majority of Jango's assault is limited to the pistols and the jetpack missiles. And again, Montross is (apparently by choice) not fighting Jango on equal terms, because Jango still has a jet pack, while Montross has the skiff on auto-pilot. Jango only wins this round because he disables Montross's skiff and chooses to leave when Zam Wessel finally shows up with Slave I. How big of a victory was this for Jango? Upon leaving Malastare, Montross does seem royally pissed off, but before the fight he also said he was getting bored by all these duels. It's tough to say who really got the upper hand here.
The final fight illustrates Montross's best skills as a fighter. He waits until the very end of his hunt to break out the jetpack, and he fights with exponentially more aggression than ever before. Chances are on your first play-through you got owned; I know I did. There is a bit with the dialogue between Jango and Montross that the reason why Montross has not been using the full arsenal of Mandalorian armor is because he "gave up" their ways, as Jango suggests. (Montross then tells Jango, "For you, I'll make an exception.") The game's strategy guide also indicates that the battle-armor Montross is wearing at Vosa's gate is "ceremonial," so it could have been something that he was saving until the very end. We are led to believe that most if not all of his previous hunts did not have him sport the armor, and certainly not the helmet and jetpack. This implies that Montross only uses the bare minimum of equipment for the majority of his hunts, likely because most bounties are not challenges for him, or pose very little of a challenge.
When serious, Montross is more than a handful for Jango. Jango, under the player's control, has to be completely evasive if he wants to have any chance of survival - and must under all circumstances keep his distance from Montross. Really the best way to take Montross down is with the heavy, two-handed gun you get earlier in the catacombs - assuming you've saved that and not used it against the Bando Gora swarmers. Missiles are good for knocking Montross off his feet, but almost every attack you have is really just a desperate attempt to whittle down his health. In my opinion, Montross, in that final fight on the moon of Bodgen, is a much tougher boss than Komari Vosa.
Would Montross have beaten Vosa?
This seems to be the primary question the author of this thread is asking. How would Montross have fared against Vosa? Would he have avoided capture? And what would this mean for the Star Wars paradigm, as another poster insightfully pointed out?
I think that Montross would have been at least as successful against Vosa as Jango was. There is a mild implication in the story and lore surrounding it that, of the bounty hunters selected for this hunt, only Jango really stood a chance of beating Vosa. Based on other incarnations of Count Dooku (such as the Open Seasons comic), it is insinuated that Dooku knew all along that Jango was the only choice for the original host (i.e. the "prime clone"). Dooku's experience in witnessing Jango on Galidraan is cited as the primary reason he wanted the Mandalorian bounty hunter. The bounty on Vosa was simply a way to fulfill Sidious's request to wipe out the Bando Gora, which was a threat to Sidious's secret plot to overthrow the Senate and Galactic Republic.
Putting aside that Dooku really only saw Jango as the choice for the clone host, and the hunt for Vosa was just a way to confirm it, we can imagine the likely scenario if Montross had defeated Jango and fought Vosa himself. I personally believe that based on Montross's skill in the final battle, and his personality as shown throughout the game's various cutscenes and in-game dialogue, that he would have certainly bested Vosa in much the same way Jango did. Vosa's strengths as a fighter are in close-range combat and in her dexterity to avoid hits (she flips around when she takes enough damage), and the primary way to beat her to keep on the move, shooting her as she runs at you - a style of ranged attacks which Montross has exhibited very well throughout the game. Admittedly, Vosa does appear to have a bit of a death wish based on her in-game dialogue (the pain and possibility of death feel good to her), and this seems mostly because she is bat-shit crazy. It can, however, explain why she tends to charge straight at Jango and leave herself open for hits when she's not deflecting blaster fire back at him. Like Jango, Montross would no doubt take advantage of this.
We don't have much to go on in terms of imagining how Montross would fare otherwise, but we do get a sense that he would be vastly more ruthless than Jango. He would certainly bring his A-game to the battle with Vosa, since he sees this as the ultimate hunt. It's not just about proving himself better than Jango; he vows repeatedly that "only one of us will claim the prize" and promises that Vosa's bounty "WILL" be his. He would be utterly savage and would show no mercy to the Bando Gora throughout the temple. However, one thing that puts Montross at a severe disadvantage is that, again, he does not sport the full arsenal of the Mandalorian battle armor. This means he would not have the flamethrower needed to get through the hordes of Bando Gora throughout Vosa's temple and the cliffs leading up to it. For reasons known only to him, Montross appears to skip much of the trek needed to reach the gate to Vosa's temple. As Jango is about to reach the final chasm before the gate, Montross's ship is parked squarely in the quagmire of the "Death Lake." (Jango, meanwhile, had parked Slave I in the moon's slave-trade hangar and went most of the way on foot.) Why Montross parked his ship in the middle of a lake is anyone's guess. Perhaps he thought it was simpler, or perhaps he simply didn't care. What we do know is that by doing it he effectively skipped over much of the encounters with the Bando Gora foot-soldiers that Jango had to overcome. Montross himself suggests that he was simply waiting for Jango to show up ("Been waiting for you, Jango. Thought you might not make it.") - which is what he really wanted, rather than go through the hordes of Bando Gora in order to get there. Despite having appeared to avoid the Bando Gora by parking his ship right next to the gate, once Montross defeated Jango, he would obviously need to deal with the Bando Gora which linger in huge droves throughout the caverns, caves, and cliffs leading up to the dark edifice of Vosa's temple. Assuming that Montross would make short work of the Bando Gora even without the vital aid of a flamethrower, once he reached Vosa his weapons and skill are in my opinion adequate enough to beat her.
It is impossible to know if Montross would have been captured by the Bando Gora like Jango was. The only reason why Jango even got the chance to battle Vosa at all is because by sheer miracle Zam Wessel made it all the way not just to the moon, but to the inner sanctum itself - and shot Jango's shackles to free him. There is a brief moment in a cutscene where we are shown that Zam in fact had an opportunity to shoot and kill Vosa herself, but because she hesitated and turned the gun towards Jango (out of revenge for leaving her on Tatooine), it gave Vosa the chance to pull her lightsabers, which made Zam no match for her. Without Zam's decision to free Jango, both would have died, or they would have become brainwashed slaves of the Bando Gora. Would Montross have gotten the same benefit of Zam's help had he been captured? It's difficult to say. I lean towards that Montross is brutal to a point that Jango isn't, and he would have been more likely to avoid capture. Montross was ultimately killed by the Bando Gora, but this is because Jango wounded and possibly even crippled him in the arena at the gates to Vosa's temple. Had Montross defeated Jango, I think he would have savagely wiped out any Bando Gora who came after him (since he can't skip over any of them), and when facing Vosa, he would have allowed her to pull her lightsabers, because anything less he would have seen as unchallenging and dull. The fight, at that point, is anyone's guess. I lean towards Montross primarily because, in my opinion, the sheer aggressive style and level of ferocity he exhibits in his final boss battle is vastly more intense than Vosa's, and it is very possible for the player to straight up defeat Vosa on the first play-through. By contrast it is almost impossible to beat Montross in his last duel on the first run. You are extremely likely going to lose at least one of your lives and watch the special ending where Montross stands gloating over Jango's corpse. (Vosa has a special ending too if you lose to her, but to this day I know people who have played the game multiple times and still have never seen it.)
What about the Star Wars paradigm?
Almost everything about the Star Wars paradigm changes if Montross wins. First, we don't even know if Montross would have accepted Dooku's offer to become the clone host. Considering that Montross felt driven more by the thrill of the hunt and enjoyed killing people, it is hard to see him accepting Dooku's offer for financial reasons alone, or even for the reasons Jango did. It is possible that Montross would have accepted because in his mind it would have been neat to see an entire army based off himself. It would be the ultimate validation that he never received from the Mandalorians, who never gave him the opportunity to lead or even fully trusted him, instead choosing a young Jango in his 20s over the battle-hardened and immensely experienced Montross. One could argue that Montross never had the temperament for leadership and would have easily led the Mandalorians to ruin worse than Jango did, and as such it's curious if Dooku would have even considered Montross a good choice for the clone host at all. Certainly Montross's skills and abilities in combat would make for a particularly ruthless and impressive army of clones. On that count it is hard to say that Dooku (and by extension Sidious) would outright dismiss Montross on those attributes. As we saw throughout much of the Star Wars saga, even in Episode II, the clones were really more watered down versions of the original host. The clones of Jango showed very little of his moxie and badassery. In terms of combat, Montross's clones could be seen as an improvement, but Montross, who had little penchant for following orders, would have passed down a myriad of undesirable traits to his clones as well.
Let's assume that Montross's clones are just as ruthless as he is. The army of the Republic would be infinitely more fearsome and the clone war would presumably have ended much more quickly. Ironically, it is Dooku leading the forces of the Separatists, under Sidious's instruction, and so the clones are fighting against the man who led to their creation. (We know that from Order 66 the entire thing is merely a ploy to ultimately turn on the Jedi and establish the Empire.) Jango chose to continue working with Dooku and became something of his bodyguard. Would Montross have done that? Montross was even more of a lone-wolf than Jango, so it's hard to see him working as a lackey for Dooku in any capacity. Montross would also have had almost certainly no interest in acquiring an "unaltered" clone as Jango had requested, so the character of Boba Fett (or anything resembling him) would have vanished from the Star Wars paradigm.
If Montross is still alive by the time of the original trilogy, he would have been too old to go after Han Solo or pursue any of the bounties that Boba did, so it stands to reason that those would simply have been done by another bounty hunter. Keep in mind that it was the Empire, not Boba Fett, who captured Han. Boba merely tracked Han and the Millennium Falcon to Cloud City. That could just as easily been done by another bounty hunter, such as Bossk or Dengar. So the notion that Han would have been killed instead of being incased in carbonite ignores the fact that Montross would have been in his 80s or 90s at the time, if the person is insinuating that Montross would have gone after Han himself. Without the paradigm of a clone like Boba Fett, we have to assume that anything done by or involving Boba Fett would either not have happened or would have been done by a rival bounty hunter. It is doubtful that Montross would have wanted a "son" the way Jango did. There is no evidence to suggest that Montross shared Jango's desire for an apprentice or protege, even if we assume that Montross would have accepted Dooku's offer to become the clone host. Montross would probably have been delighted to see clones of himself wreaking havoc across the galaxy, but that doesn't mean he would have wanted a son.
Similarly I can't see Montross continuing to work with Dooku in the same capacity that Jango did. Dooku would have to continue to offer Montross high profile bounties against insanely tough opponents for Montross to remain interested. While it is unlikely Montross would have been present for the Battle of Geonosis, it is possible that he would have had confrontations with the Jedi Order once they found out he was the original host. They would have wanted him for questioning to get to the bottom of the mysterious origins of the clone army. If either Obi-Wan Kenobi or Mace Windu battled Montross in that capacity, it would be difficult to say who would emerge victorious. Jango fared well in his duel with Kenobi because Boba was helping Jango by attacking Kenobi with Slave I during the fight. Jango had no outside help in his short duel with Windu, and because Jango's jetpack was damaged and failed, Windu was able to get in close and cut off Jango's head. It is hard to see Montross finding himself in similar situations to Jango. While it is possible that he could have stayed on Kamino and made it his home as Jango did, because the cloners needed more blood from the host (I guess?) and Montross would have maybe stayed to train some of the clone army (possibly?), the more likely scenario is that Montross would have gotten bored there. He almost certainly would have no interest in helping the Separatist cause, even if Dooku promised him huge amounts of money to act as a glorified bodyguard at Geonosis. However, if Dooku would have sent Montross to kill a high profile Jedi, such as Mace Windu or Yoda, we can easily see Montross taking on that kind of challenge, purely out of the thrill of it. He would definitely see it as a challenge worthy of himself. The question then becomes whether Dooku would have done that, when in the canon he never put prices on the heads of the Jedi Council, as far as I know.
If Nute Gunray had tasked Montross with killing Padme Amidala, we can safely assume that Montross would have easily succeeded if he decided that assassinating a Galactic Senator was worth his time. Jango passed off the same bounty to Zam for reasons we don't know why, and when Nute demanded that Jango kill Padme in the arena on Geonosis, Jango didn't exactly jump to action. We have no clue as to why Jango acted this way. Maybe he didn't respect Gunray enough to do it, either because of his own code of honor or possibly because Dooku simply told Jango that Gunray was a mook. Whether or not Montross would have felt differently is impossible to know. Had he accepted the bounty on Padme, he certainly would have been more interested in completing it if he knew the Jedi were protecting her. So it's doubtful he would have shot at her ship the way Zam did in the opening scene of Episode II. While that is an efficient way of killing, Montross has shown to be more interested in hearing his prey beg for their lives, as he told Jango in their final fight on Kohlma. As such, he would have wanted to kill Padme with his own two hands. This, of course, would mean that Luke and Leia are never born, which potentially means that the Rebel Alliance never defeats the Empire.
It is interesting to think about the butterfly effect that would have happened just from the simple question of Montross killing Jango and Vosa. The question that then needs to be asked is whether Montross would have stuck around for the events of the Clone Wars. Jango did, for his own reasons, until his death, but most bounty hunters did not seem keen to get involved unless there was a substantial profit in it. Montross, who by his own admission has never been interested in money, would have needed to have a more thrill-seeking reason to be involved in the plot. The only reason I can see is if Dooku or Sidious tasked Montross with murdering incredibly challenging, high profile targets. Whether or not Montross would have survived Anakin's rage if he killed Padme is a debate for another time.