Okay well first off the Ps2 has the best selling game series (MGS, GTA, Final Fantasy, Resident Evil... etc)
But the XBOX does have the best specs to it, it's the most powerful console, but game wise the Ps2 has a better variety.
The Gamecube has pretty good specs, but the worst game variety out there, first off it doesn't have nearly as many games as either XBOX or Ps2 plus the company is heading downhill because the XBOX and Ps2 are getting WAY more sells than it.
IMO it's a tie between XBOX and Ps2
Ps2 has the better variety of games
XBOX is more powerful
Honestly though if you're a real big gamer, the best gaming machine is the PC if you have the right hardware...