in terms of hardware the gamecube has the 2nd best graphics chips and accelerators.
Xbox is first, and PS2, which is the oldest is last.
As for the games themselves, it all depends on what game it is. For most multi platform games(xbox, GC, PS2 supported) the PS2 will look weak, while the Xbox will look marginally better then the GC. Very little difference.
BUT! IF you get a crappy looking game, it will look crappy on your tv as well.
Another pro for GC is that some games are 480P supported. I know some xbox games are HDTV supported with the kit, but i dont know about 'as is' 480p games.
