Having owned both the Xbox 360 and PS3, I think I'll be staying loyal to Microsoft - I just prefer the online setup to that of the PS3. I mainly used my 360 to play online and although it does cost to use live on the 360, I feel as though it was all integrated so much better.
Having said that I'll probably end up with neither as the other half wants me to keep my 360 so she can play Grand Theft Auto!