I think it really comes down to what system has the exclusives you like better. Because other than that, I see no reason you couldn't enjoy either of them.
Also, I believe that the 360 is cheaper. The games certainly are.
Anyways, as Unbreakable probably already said, Xbox Live is the backbone to Xbox itself. PS3 cannot live up to the status of it, even being free. There is so much more to Xbox than you will realize. Such as the higher connectivity to websites and radio stations, plus higher tech microphones designed only for Xbox Live. Not only this, but there is so much more.
I've never taken time to sit down and play Ps3, and what I said above is the reason why.
* Updated game trainers and cheats daily
* Get notified when new cheats are added
* Request which games get new trainers
* Priority support with any problem