Owned all three and Gamecube was by far my favourite, although I did have a lot of fun with the PS2 I actually picked one up towards the end of its lifespan when my Xbox packed in so many of the earlier games that had good reputations on the system felt a bit dated at this point.
Gamecube had the best controller and some of the most brilliant games, Wind Waker remains my favourite Zelda game and the most charming game I've ever played and Nintendo put out plenty of other great first/second party games such as Smash Bros, Animal Crossing and Paper Mario: TTYD, plus others that never got the credit they deserved like Eternal Darkness, Luigis Mansion, Jungle Beat and Chibi Robo. Despite the critics it had some great third party content as well like Rogue Squadron II, Monkey Ball 1/2, Skies of Arcadia Legends etc. Wonderful System
Xbox was a major disappointment for me, got mine as part of some mega deal at Toys'R'Us with a load of games including Splinter Cell, Halo, Blinx the Timesweeper and Munch's Odyssey. Splinter Cell wasn't up my street, though it was a very impressive game technically I just found it frustrated, Blinx has to be the most awful and broken platformer I have ever played as well. Halo was great fun and playing it in co-op with my mate made that christmas, but I found Halo 2 to be the most disappointing game of the generation and there was very little that interested me towards the end of the consoles lifespan, 360 gathered dust like nothing else.