i wud say xbox 360, reasons:
Cheaper @ 130 GBP here in the UK
PS do not have too much exclusives, whereas 360 have halo, crackdown, fuzion frenzy, too human etc
although you have pay which is a downside, but still works out cheaper than a ps3, xbox live i find is betta den PSN, PSN i find is deserted
exclusive DLC for GTA IV
im no fanboy tho, i own both consoles, and thats my opinion