Im gonna state some good and bad facts about each.
XBOX- When a game comes out for all 3 systems (PS2, XBOX, and GameCube) it will probably be better on XBOX. But the only good game I have seen is Halo. And Halo 2 looks good. On the downside it is large, heavy, and it doesn't have a cooling fan. So if you like playing for long hours, don't get XBOX.
PS2- This is the system I know least about so I may not be right. PS2 is the best selling system out there. But it doesn't have much good games. GTA is the only good game it has.
GameCube- It is small and is easier to take places. It has great games and easy-to-learn controls. It can't play DVDs or CDs (unless you buy a Panasonic Q GameCube.) The Panasonic Q lets you play regular GameCube games and lets you play DVDs and CDs. The last I checked though it costed $500. But I don't know anymore. GameCube has been critized for being kiddie. But I guess that is in the eye of the beholder (Ah im using wise man stuff.)
Psst! Psst! Hey guess what...
I like firetrucks, and pink ducks, and rubber bands, and pinball, and pocket lint, and...