Warrior beats Gladiator almost every time the possibilities of tactical conflict exceed the rules of engagement. That said, a gladiator is often far more expert at maximizing the damage dealt by their preferred weapon.
As a soldier, John Rambo is likely to rely on a variety of martial arts as source material, even for what amounts to a bare-knuckle brawl. This will make his own actions harder for Rocky Balboa to predict, and allow him multiple means to deflect and reduce the effects of blows received.
As a boxer, Rocky will have a much harder punch, likely more "pure fighting" stamina in a toe-to-toe battle, and the ability to take more direct hits and shake them off.
What it comes down to is this: can Rambo land enough punches (and I assume for fairness' sake, kicks) to knock Rocky out quickly, before he himself is worn down by a focused and unending knuckle-attack, and/or get inside Rocky's attack radius, and incapacitate him via some other means (choke out, arm/leg locks, etc).
We can even look to Rocky III for some hints on this: http://www.youtube.com/watch?v=2…
It's pretty clear when Rocky fights Thunderlips that:
- The gloves impair his ability to damage his opponent significantly
- pure boxing presents too many fighting limitations – throw rocky to the ground (or pick him up above your head), and his fighting force is greatly diminished.
- Rocky's arms and chest are his strengths – while Thunderlips is unable to choke out Rocky, Balboa's much smaller "pythons" seem to have a greater effect on the wrestler when an improvised sleeper hold is attempted
Overall, the idea that Rambo would win "most of the time" is probably statistically correct given his more fluid fighting style. That said, in a "fair fight", it's hard to imagine that Rocky wouldn't emerge victorious, due to his greater ability to give and receive pure pugilistic hurt.
On a more personal note, and given recent events, I'd just like to say that this fight would sadden me to no end – because when Rambo and Rocky fight, the terrorists will truly have won.