Best ones:
Wolverine X-Men Origins for PS3.
X-Men Arcade.
X-Men 1 & 2 for Genesis.
X-Men: Age of Apocalypse for SNES.
X-Men Children of the Atom for arcade and Saturn. (Haven't played the PS1 version as i heard it sucked)
X-Men Mutant Academy for PS1.
X-Men Legends 1 & 2 for PS2 and Gamecube.
Marvel vs. Capcom for all systems.
Street Fighter vs. X-Men for all systems and Arcade.
X-Men Dimensions for Gamecube.
Marvel Alliance for Playstation 2.
Fair:
Marvel Alliance 2 for PS3 and Xbox360.
Wolverine's Revenge for PS2 and Xbox.
Medicore:
Wolverine for NES. (An improvement over the horrible LJN X-Men game but at least it was playable but i didn't like how if you use your claws it can drain your life for you have to kick and punch instead, medicore i say)
X-Men for Gamegear.
X-Men: Wolverine Adamantium Rage for SNES and Genesis.
Worst:
X-Men for NES.
X-Men/Spider-Man: Arcade's Revenge for SNES and Genesis.
X-Men The Official Game for any system.