Disclaimer: I actually own all three major systems.
I would agree that the original Xbox controller was too bulky, but the s-controller is better than a PS2 controller, IMO. The gamecube controller is very unintuitive. While I do like several games on gamecube, I feel that its the worst VALUE of the lot. There are only a handful of games that I liked, like Pikmin, Zelda: WW, animal crossing (

) and a few others. My personal favorite is the xbox, as the games seem to have a feel of greater gameplay. Halo, KOTOR, Morrowind, and TW2004 all got the crap played out of them in my system. And have you seen the previews of Halo2 and Fable? Unbelievable. PS2 is certainly the safest bet of the bunch. It's a solid, but not outstanding, system, and has a massive library of games, ranging from abysmal to awesome. The GTA's are easily one of the best reasons, except now they've been ported to other systems. Actually, Gamecube probably has more exclusive games than any of them. The thing for me is that I'll never see a game on PS2 that can't be played on Xbox. (omitting license agreements) The same can not be said in reverse. Don't you think they would have released Halo for PS2 if they could have? The system just can't handle the game and the graphics.
I think I'm done, for now.....
EDIT: by GT3, I think roddy means Gran Turismo 3. If that's the case, then yes it is out, and yes go get it if you enjoyed version 2. Some of the same tracks, some new ones, many new cars, and now you can win F1 cars!! Once you win one (doesn't matter which one) it's all you will drive, except for the specialty races. (FF challenge, etc)