OK - first decision is whether you want blu-ray .... now? Personally, even if I had one, would not be buying blu-ray titles (as I never really bought DVD's). Most of the hi-def stuff I am interested in is played using a different player (HTPC or Sky HD etc.)
If you answer yes, the PS3 all the way.
If you are not fussed .... 360 without a doubt. AND NOT BECAUSE ITS BETTER! I am tired of reading these threads. This is totally a much of a muchness. 360, much cheaper and more titles. PS3 fewer titles and much more expensive. 360 much larger community, PS3 smaller community. There are games on PS3 better than 360. There are games on 360 better than PS3. Hardware spec - bit like PS2 vs. Xbox 1. PS2 came out first, Xbox arguably better console ... PS2 much larger fanbase, popularity etc etc .... although it did not stop people chosing Xbox over PS2. I think its role reversal this time round, although PS3 has not developed to be visually better ... yet. Although a new xbox will come along that will be better .... and then back to the forums for a good old fanboy rant

I have played/seen both on massive Sammy screens and its is horses for courses!!
Online - sorry, but lets be honest here, the 360 online experience is miles better but thats because is much more established. PS3 give it a few months ... gonna be the same.
360 does have the rewards/achievement system which is a nice addition to gaming.
You can get a xbox 360 with two brand spanking new titles and an extra controller for a little over £200. A mate of mine bought a PS3 from Game (on a weekend they had a special on, about 2 weeks ago) and once he had picked up 4 titles (some bundled in - of which only one is really an brand new title, rest are semi old) and an extra controller he had spent £440. Imagine having £240 to spend on games after buying a 360.
But then hey, if most of your mates have got a PS3 .... you are hardly gonna buy an 360 now are you!?!
Just buy what most of your mates have got, sort out the blu-ray thing in your head and just enjoy whichever you choose. They are both cracking machines with some seriously tasty gamage!