As someone who developes games for both PS2 and XBox, I will tell you that many developers will drop PS2 the second it isn't the world leader anymore. While many aspects of the machine are pure genius, it is a bitch and a half to make games for it. XBox (and Gamecube, for that matter) is a far superior machine in most aspects, even with out the hard drive/ethernet. But the only thing that really matters is what system has the most fun games. PS2 has such a solid foundation of games, I think it is the best to buy for your self right now. In one years time, things will probably be different. Once Sony and Microsoft have their networks up and able, and XBox has a year's worth of titles availible, it might very well edge PS2 as the leader. Both PS1 and PS2 were more or less shit (games wise) for the first year, the BAM! quality titles just came from everywhere. XBox on the other has two or three instant classics at LAUNCH. Amazing. I admit I more or less baught an XBox just for Halo, which I had been waiting for from 3 years now.
Whichever one you buy, there will be great games. PS2 is the one with the best liberary NOW, but XBox is well prepared for the future. I have both, love both. They are both great machines.
P.S. for those of you that hate the XBox's shitty controller design, I played with the Japanese one and its much better. Word it they will switch to that one when all the U.S. ones are sold. Thank god!