So far, I have both the GameCube and PS2. I play GC more because of Smash Bros. Melee(one of my top fav. games of all time). Plus, I'm looking forward to Zelda, Mario, Metroid, and I'll give RE a whirl when released. I'm also thinking about getting Sonic.
I got PS2 to replace my PS1 when it broke down. (how convienient, it breaks down when the second one is released. Since then, I've mostly purchased PS1 games. I like Gran Turismo and NBA Street. But, since I've had PS2, I've played mostly MMX5, MMX6, and RPG Maker.
The X-Box so far doesn't appear to offer much to me in terms of software. Most of the games I see coming to it, will either be released on GC or PS2 or even all 3. Why by an X-Box when I can get the game on a system I already own?
Besides, my favorite games are nearly guaranteed to be on GC. Mario, Zelda, Sonic, Sonic Team games, and Metroid. The question is, where will Mega Man, Street Fighter, and Castlevania be released. If either GC or PS2, I'm safe.