Well although I'm more Sony inclined, I'm not going to say until I've played both.
Let's face it - it's soooo stupid arguing about which is better before anyone's seen stuff on actual completed hardware. Both Sony and Microsoft have been showing demos using PCs not the actual hardware and NOBODY will know which is "better" until a very long time. Infact, it doesn't matter which is more powerful, it's the games that count, and to get the best, you may as well buy both.
The problem is that people who are Xbox or PS2 inclined now, will probably go for the next-gen version of what they prefer at the moment, when they'll both be completely different from what's out now.