I have to say I prefer PS2 the best. I know it can't stand up to the Xbox in terms of graphics, but there are so many more games I'd rather play on PS2. For example the Gran Turismo series. It is undoubtadly the best racing simulator game on ANY console, and for that reason alone I would pick a PS2 over an Xbox. None of the games really interest me.. apart from a couple that are available for PC anyway.
This argument really does come down to personal preference though, and if you're undecided on which system to get, it's not always the best option to ask a group of people their opinions. You MIGHT just miss out on the console you really want.
I voted for PS2 obviously, but in doing so I am not trying to say that the PS2 is the better console, just saying it is the console I prefer.