These threads are tricky because all the ps3 owners will tell you that the ps3 is the best and the 360 users will do the same. Flat out I'll tell you now that whichever decision you make will be the right one because both systems are fun.
I'm pro ps3 because it's features are more in-tune with my entertainment demands. I have an hd tv, so the blu ray player is pretty much a must. I'm a bit of a quality whore, so I haven't even considered buying a dvd in almost a year. In my opinion the system is worth it for a blu ray player alone.
Built in wifi was also a big deal for me. The 360 requires a $100 accessory to use a wireless signal, so that immediatly eliminated it as an option for me.
Rechargable controllers is more of a nitpicky thing. I'm not sure if the elite comes with these now (the older models didn't and I had to pay $30 for a battery pack).
The games arguement in my opinion was more of an issue last year. Ps3 didn't have a ton of games and the multiplatform versions tended to be stronger on the 360. Lately we're seeing a shift where the games are much more equal when they hit both systems, and in some cases the ps3 versions are showing minor improvements even. The library has grown to the point where there are enough incredible games for the system that I doubt you could play them all.
Live is incredible for social organization, but personally I'm finding the psn is slowly improving. It probably will never be outright better, but it is free (something else that is huge for me as online gaming isn't normally my thing ... well, before nhl 09 of course). As for games on the psn compared to Live, I prefer the psn games. That's more a preferential thing as both systems have their share of quality downloadables.
Ps3 does lack in the online department I find mainly for it's lack of mic users (as the system does not come with a mic like the 360 does). This does have it's advantages as when using live you can often find yourself balls-deep in ######bags and 13 year olds hurling racial slurs at you that would make Tupac cry. Regardless, it's annoying when you're playing an online game and nobody is talking or communicating.
Check out my LittleBigPlanet thread to learn my #1 reason to buy a PS3.