My own opinion..

PS3:
Free online
large content games does not need to swap disc
Exclusive titles are more popular on ps3
Can play bluray dvd movies
controller fitted with rechargeable batt
expanding hdd is cheaper

xbox:
Online play hv to pay
recharge batt not included
controller design is firmer
large content games hv yo swap disc
most multiplatform games look bettet on 360
Hdd expansion is expensive using Ms official product