I have alll three, and I can safely say the PS2 is my favourite.

1. Wider range of games.
2. Best controller.
3. Cheapest console to buy for. I've come across (and bought) more sub-$30 AU priced games than on GC or Xbox.
4. Excellent all in one package. Plays PS2, PSX, music CD's (CD-R's too), DVD movies and sometimes I can even get it play CD-RW's

My only complaint is the lack of in-built multi-tap.

Xbox would be a close second, but I haven't that for as long so it's yet to prove itself in any significant way (although network Halo is a BIG plus!).

GameCube's a distant third. Terrible controller, poor range of games.