The PS3 never got the Heroes/Villians DLC packs that the 360 got. That alone gives the 360 a bonus of Hawkeye, Cyclops, Sabretooth, Venom, Dr Doom, Magneto, the Hulk, and Nightcrawler. PSP had Black Widow, Ronin, Hawkeye, and Captain Marvel.
And then there's the PC version, which, through the magic of Mods, has just about every marvel character ever thought up in it.