Both are pretty good. The PS2 certainly has some serious contenders on the games front though, including (but absolutely not limited to):
Shadow of the Colossus
God of War I and II
Katamari Damacy
Metal Gear Solid 2 and 3
Ico
Kingdom Hearts I and II
Ace Combat 0
Guitar Hero I and II
Resident Evil 4
Grand Theft Auto series
A lot of the PS2 games tend to be a distinctly different flavour to what defined the Xbox though, so really I'd look at the classics for both and see what draws you more. If it were me making the decision, I'd leap at the PS2 like an AIDS victim at the cure for his affliction.