ive got both a ps2 and an xbox. my ps2 never sees use. i can never seem to find the stupid memory card, and i dont really like any games on it. there are a few gems for it. 'ico' is prolly my favorite all time ps2 game.
my xbox gets heavy use. its internal hdd makse game saves quick and easy and unobtrusive. plus, i use a lot of third party stuff on it (the hdd) and having it there makes it much more convenient than having to find discs and load them.
as far as graphics, my money goes to xbox. i never did like ps2 because it never visually impressed me. plus, it doesnt have halo. i think gc and p2 are pretty similar in graphics, with the gc having a little bit more pull.
xbox is the most robust straight out of the box, imo. ps2 plays dvd movies right out of the box though. xbox doesnt, you have to buy a separate dongle. i understand they did this to keep the console price down.