Real hard one to answer for you mate. It comes down to what type of games you like to play and if you need things such as Blu-Ray, etc.
I personally prefer to play on the XBOX, but many here prefer the PS3. This does not stop me from enjoying my PS3 as well though
I would advise, if you have the availability, to either hire each console or go to a friends place that has them and give the consoles a good work out. Only then will you truly know which one is right for you.
The only thing I would add concerns your internet service. If you have a high speed service with a large download quota the PS3 is a great console to have, but if it is slow and your limit is small, go the XBOX.
In my experience, and I am sure even the PS3 players will agree, the PS3 system and games have more updates than the XBOX by a mile and the downloads are in many instances bloody huge.
The same game on XBOX updates in a fraction of the time.