As lightning said, each have their own perks and faults. In particular PSN is free, which is always nice. However the gamers seem to be more serious (Having forked out significantly more than a 360 would cost), but on the plus side there are fewer squeakers (8 year olds screaming profanity). However it seems more problematic and laggy. Live has a more sociable atmosphere to it, and has better exclusive games than PS3 and mountains of classic arcade games adjusted for online play. And with the New XBox Experience coming november, I can only see it improving.
So yeah, live gets my vote for sheer fun factor =]