Power is not the be-all and end-all of a gaming console. Remember the 3D0? Probably not. It was powerful and cool, but languished in the market.
Ok, better example–the Dreamcast. It was more powerful than the PlayStation, had a ton of good games, was well-liked…and failed way before it was supposed to.
In terms of sales, Sony has already won this round of the console wars. The PS2 has sold millions more worldwide than the X-Box, and the X-box is practically ignored by Japan, which does not bode well.
But in the end, a lot of games will be out for both. Practically every sports game comes out on both, as well as a lot of major titles. You pretty much need to look at the few exclusive titles (Grand Theft Auto, Halo, etc.) and decide from there.