I have a PS2, because I like the titles they produce more than the others. Also, finding the games are relatively easy to find in stores and they are slightly cheaper than the others after they've been on the market so long.
If I were you, I'd get a PS2, or an XBox. I also like those, if you want to play online it might be better to get one of these as well. The Gamecube is by far the cheapest, but it's because it's way behind in graphics and gameplay. It's just a cheap Nintendo system.
I'd say, get PS2. I have one, and I enjoy it very much. Plus some good football games. And the WTA Tour Tennis game is excellent. (Then again I haven't played Topspin on Xbox yet either). Any stores you can demo both systems at? I know here a few places let you rent a system for 2 nights. That might be worth a try. If not just go in an electronics store and play each of them all day until you decide.
hmm i say ps2 cos i have it and i like the games on it(pro evolution 3 for football and wta tour tennis for tennis). though an xbox would be good too...how about buy both ..or u could just ask one for a present