Your best bet is to look at the games you would want to play. Halo was fantastic, Max Payne was tolerable on the XBox (NOT on the PS), Super Smash Brothers Melee was fantastic on the GameCube (as was the Star Wars game… tough, but you only need to get as involved as you want… there’s hidden stuff to look for if you’re in the mood, but it isn’t absolutely necessary to win). Soul Calibur 2 should be coming out on all systems, so that’s the fighting game to watch. The PS has FFX and FFXI going for it, but those are pretty involved RPGs so probably not your cup of tea.
I dunno, the PS2 is a decent choice… I wouldn’t say you’d be disappointed. My problem with the PS2 is that it floods the market with games that simply don’t impress me. XBox I haven’t paid much attention to, but god Halo was so impressive I can barely stand not owning one. I got a GameCube because it was cheap, has a few good games available now (I don’t play much, either), and looks to have some more great ones coming (Metroid, the entire RE series, Starfox, Zelda, Eternal Darkness…), so that’s the one I’ve really been following.
I’ve heard so many good things about GTA3 that I must be asymptotically approaching a state of virtual leprosy for not having played it (and, worse yet, not having a desire to). I say head to http://www.videogames.com/ and spend a good three days looking over games that sound interesting on each system. Unless you play video games 24/7 the difference between the three systems is, IMO, only dependent on what games you want to play.
Look to the games and all will be revealed. PS and XBox both have some good racing games, and I think the GC is also coming out with some good ones. All three have skateboarding/ snowboarding games which seem to be popular. IMO the XBox is prepared to go the distance in length of service, the PS2 has the added advantage of playing PS1 games (and there are some goodies out there even if the graphics might seem dated), and the GameCube seems to have the usual Nintendo franchise games behind it (which is usually enough to sell me).
My opinion, then, is essentially: it doesn’t really matter which system you get unless you don’t have a DVD player. You’ll be happy with all three, I think.