An age old argument my friend.
Search the forum using "XBOX PS3", without the inverted commas. The discussion has come up several times.
XBOX Live (online ability) you pay for
PSN (PlayStation Network) is free
Essentially, it comes down to whether the system has the games you would like to play.
PSN : jamem69
XBL, WindowsLive, STEAM, EA/Origin: jatcave