I have no idea how old this thread is or anything. For some reason I don't see any of that on the website. Decided to throw out my 2 cents on the subject as I am a nerd who has studied stuff like this for a long time and likes to run mock battles in my head.
Contrary to the general strong current heading both to clear cut victory this area is kind of grey but still somewhat strongly favoring marvel. Keep in mind I try to remain as unbiased as I can in these discussions. First I will take the less grey and much shorter to explain opponent of Juggernaut.
Juggernaut: Firstly yes, one of his express powers is that he is invincible. As we have all seen him injured and sometimes even incapacitated (probably more accurate to reverse those two) then logically we can deduce that the definition of invincible in this case refers to essentially being unkillable. Now for a couple anal people on the board who's names I conveniently forgot and insist on specific canon in comic references, no I don't think at any point in the series they ever expressly state his powers(although it is stated on the marvel wiki which I believe has it's own references and I THINK on the marvel site itself). Which means we need one or more secondary strings of logic to reinforce this idea. In MOST fictional universes, a soul is a unique thing amongst humans and other lesser sentient races, it's supposed to be representative of free will and limitless potential. Now USUALLY more advanced or powerful beings/races are supposed to be devoid of a soul for various reasons one of the most important being that they are more like programs whose power is invested to serve a specific function to the universe regardless of what that is. Galactus for example is invincible out of necessity if I remember correctly, he is a fundamental part of the universe. This forced nature deprives them of free will and fundamentally makes them more like an incredibly advanced AI than a person. The reason why this would be relevant is because Juggernaut is not a mutant but the avatar of a God. His power is an investiture by a powerful elder god of the multiverse. Technically, at every conceivable level, he has been transformed and is no longer fundamentally human. However this is VERY debatable on many points, power boon doesn't necessarily mean loss of soul, there is no canon proof that this is even the case, he doesn't display as much "programmed" behavior as some "higher" beings do, etc. However, at the very least this divine nature stands to reason that he is either reinforced beyond harm, very probably could qualify for that super soul category, or simply out leagued (sorry but it is not only reasonable but assumable that a godhead would simply be immune to this form of attack from it's nature alone). One piece of evidence that does point to "celestial beings" not having souls (correct me if this isn't canon) is that humans can reincarnate but these beings die for good. For the specifics on his invulnerability and the part where it says his soul merged with a gods (which i think would make a super soul) please check out marvel wikia search cain marko.
Hulk: Since it was Hulk stated and not Banner/Hulk, I will exlude any methods of killing banner or reverting the Hulk. I have some trouble admitting that Hulk is more "killable" under any circumstance then the Juggernaut as he has always been a personal favorite of mine. It's the simplicity of a virtually unbeatable strategy. I keep getting madder and stronger until I win, and yes enough strength can start breaking reality and concepts. Having said that, this is still somewhat grey. While the Juggernaut is black and white clear cut beyond killing, the Hulk is just REALLY hard to kill. If we took the Hulk from a purely physical perspective. There is no cut and dry explanation on the full nature of the durability or regenerative capability of the hulk. However, as he can regenerate lost organs and has a regenerative speed to put that chick from heroes to shame, it is safe to assume that he is a perfect replicator capable returning to full form in relatively short order from something potentially as small as a finger or single strand of dna. Since we all know Hulks physical virtual indomitability I feel it's very safe to say that that soul killer technique is the only realistic shot of killing the hulk, but how capable is it? For one thing, I doubt the soul has a very solid definition. Is it an innate spark of divinity we are born with? If so, the hulk was not born, he spontaneously came into being. Is it a culmination of experiences that catalyze into a consciousness? If so, he is perma-stunted mentally and has more in common with animals than people, and therefore may not be capable of developing spiritually. Would Hulk even have a soul? Bruce Banner is the "real guy" where as Hulk is a splinter personality created to cope with a power far to great for his mind to handle, hence it's childishness (humans are not meant to be Gods after all and are not mentally equipped for that kind of power). But even if we assume all of this to be false well, he was STRONGLY hinted at being more of a God than a human or at least in a proto godlike state as he was able to move Thor's hammer which is supposed to not be a matter of physical strength regardless of how vaunted. This would almost certainly mean not possessing a soul, possessing a super soul, or simply being closer to divine in nature and inherently immune like I posited the Juggernaut may be. However, a problem with the Hulk is that, in a world of writers that change character power levels and back story whenever it suits them, he is still one of the most vaguely written in terms of power nature, origins, limits, etc, and one of the most inconsistently portrayed in terms of power level and abilities.
In the end, I would have to say VERY likely that Juggernaut wins and closer to 50/50 with the Hulk.
Isn't juggernauts powers given to him by the the crimson gem of cyttorak and pretty much his mind body and soul is property of Cyttorak as his avatar of power. I'd imagine his soul is protected as such but sadly nothing i can remember has happened to him where his soul has been under attack.
Only thing close is the fear itself arc where he was possessed by the power of one of the hammers of the serpent and unlike the others who picked them up actually could of resist and rejected the hammer due to his cyttorak enhancements and patronage but allowed the hammer to take him instead.
Not sure if that is even note worthy for this fight but it's the only thing I could think of ATM.