I prefer PS3 for a couple of reasons.
First, PSN vs Xbox Live. PSN is free with no ads, while XBL is the opposite. Yes, PSN has been hacked in the past, but I find it's never for too long, and Sony makes up for it with freebies. In addition, if you do pay for the service (same price as XBL), you get a substantial amount of free content. I'm talking hundreds of dollars worth of games and discounts.
Second, Exclusives. I'll pull out the top two IMO for each, so PS3 has Uncharted and inFAMOUS, while 360 has Halo and Gears of War. While all four are great, I personally feel inFAMOUS wins this category with the rest duking it out for second. I know this is narrow, but even if I widen it out I'll only include more great games with more controversial conclusions.
I'm not giving him cake! I'm assaulting him with cake!