I don't play console games. The only upper hand that the PS3 has over the Xbox 360 is the built-in Blu Ray player when talking about hardware. If you need/want a Blu Ray player, then PS3 it is.
If that is not a major concern, then focus on the types of games offered by each system, especially exclusive titles. That should be your primary concern.
For online gameplay PSN is free while Xbox Live is $60 per year. It appears that even though Live requires an annual subscription, many console gamers prefer Live to PSN. Probably due to more activity and better connections, but that's something you need to research.