PS2 is great if you like fighting games and sports games.
Tekken4 is amazing and is for PS2 only. As is Virtua Fighter 4. Both are awesome games.
Plus you can mod the PS2 and play import games or make "back-up" copies of your games.
The Xbox is another great choice, Microsoft goes off and buys lots of small game developers and has them make games only for Xbox. Halo is a good example of that.
My buddy has the gamecube and I just don't see the interest in it. The new Metroid may make me eat my words, but so far most of the games seem for a younger audience.