There are lots of factors to consider. The ps3 can have a larger hard drive installed in it very easily and cheap, it uses a laptop hard drive, so is great for media. It also has blu ray, which is far superior to dvd in many ways. Also, there are the console exclusive games, like halo, gears of war for xbox, and gran turismo 5, and uncharted 2 for ps3 to name a few. Most games come out for both systems, but i think the xbox usually has the better ports, as it is easier to program for. The xbox also has a lot more games, and has been out a lot longer. Then there are the reliability issues. Xbox RROD is well known, but the ps3 has started having problems caused by a build up of dust heating the console, causing the soldering on the circuits to fail, although this is pretty rare, compared to rrod. People have been saying for years that ps3 is the more powerful machine, that developers just need to get to know it a bit better, then we will see the console dominate. But, its been out a while now, and the consoles are still very close. I have the ps3, the big deciding factor for me was, blu ray, and the media capabilities, as well as the up coming gran turismo game. But i would be very happy with xbox.
What ever you get, you will love it.