First off, when you're deciding a versus match with game characters involved, don't EVER trust game mechanics. Rely only on cutscenes; those occurrences are more easily quantified. If you relied on game mechanics alone, then almost nobody would ever be able to beat Sephiroth because of Supernova, but logic tells us that it's an illusion and that he didn't actually nuke the hell out of the solar system, since the planet's still there in the ending.

However, even normally, Sephiroth and Cloud beat the hell out of anyone except for insanely high-powered combatants like Q, Lensmen, some of the stuff from the Culture, or high-level Jedi. This is judging largely by the mechanics present in Advent Children. Sephiroth possesses telekinetic powers strong enough to actually alter weather patterns, and his sword can hack through large chunks of FFVII's equivalent of structural steel, which is likely somewhat stronger than what we're using at the moment, considering the sheer size of Midgar. Cloud also apparently possesses a degree of telekinesis; he wouldn't be able to pull off the gravity-defying moves we see him do in Advent Children if he wasn't able to exert telekinetic force to keep himself in the air for prolonged periods of time. He was also able to withstand the sheer energy of a presumably city-destroying blast; considering the size of Midgar, the blast summoned by Bahamut Sin would have to be substantially more energetic than even the most powerful nuclear weapons we have currently (the record holder so far is Russia's 50 MT Tsar Bomba device developed during the Cold War). This telekinesis may also account for why Cloud can survive falling from thousands of feet in the air without so much as a scratch. When you see crap like this happening in cutscenes and in the movie, the game mechanics of FFVII approach believability, even up to the point at which Cloud can take multiple bullets, even multiple clips of ammo before he finally succumbs. But it's still best to reside in the realm of actual physical formulae and numbers.

That whole explanation also doesn't take into account the fact that Sephiroth, and the scientists of Shinra who can do the math and experiments to prove it, fully expected that the asteroid impact would not kill Sephiroth. I don't have a screenshot of the asteroid's size relative to the planet ready for scaling purposes, but it's certainly bigger even than the one that eradicated the dinosaurs; it's visible from high orbit. The Chixulub asteroid impacted with a kinetic energy equivalent to that released by roughly 100 trillion metric tons of TNT, and it wasn't any bigger than 10 km in diameter at max; these calculations have been verified by Dr. Luis Alvarez, the leader of the team that pinpointed most of the archaeological data about the extinction, and his associates, positing a normal nickel-iron asteroid. Over 95% of all asteroids are of this type, and no soft, carbonaceous asteroid could have wreaked the kind of havoc necessary to destroy the dinosaurs without being substantially larger than the crater that's there today.

Vincent versus Batman is uncertain. Vincent mostly fights at long range with guns, and if Batman Begins is to be believed, the Batsuit blocks bullets. Vincent would only stand a chance with his ultimate weapon, or in his limit break mode.

As for Yuffie versus Kim, the winner is demented hentai fans.

I don't know enough about Captain America to make a judgment about him versus Tifa, but the idea of being suffocated in cleavage KICKS ALL KINDS OF ASS! I suppose an actual analysis would depend on whether or not Tifa has materia available. If so, then that tilts the chances in her favor, but the Cap's a tenacious and resourceful guy. He isn't one of the kings of comic-dom for nothing.