Let me start by saying I have both; my 360 is mainly used for the few exclusives I'm actually interested in (Gears, Forza, Halo). Mass Effect is now on the PS3 and there are very few other exclusives that I have any interest in. To be honest I put more hours in using the HBO GO app on my Xbox 360 then anything else. Unless something has changed the 360 has more users and you will most likely be able to find more games used and at a cheaper price. Keep in mind if you want to do anything online (even watch netflix) you will need a XBL Gold subscription. While MSRP is $59.99 you can typically pick these up for $35 if you're patient.
It doesn't have bluetooth (this comes into play when using the media remote---it's obnoxious it has to be pointed directly at the console) or blu-ray. The controllers are defaulted to run on AA batteries but you can get rechargeable packs for fairly cheap.
IMO the PS3 has a much wider exlcusive library. I am not going to get into a fanboy battle and say "better" but I think it offers much more.
The system itself has both bluetooth and a blu-ray player. Almost all games are going to be on just one discs (Versus multiples with quite a few 360 games). I liked the XMB navigation set-up better then whatever Xbox is currently doing but that might just be me.
If you can find a deal on PS+ you'll get a good ROI. Plenty of quality games are free each and every month (also decent discounts on other games and content) and as long as you keep your subscription you keep the games.
I think at this stage in the lifespan the PS3 offers more but if you're just going to casually game and are only interested in the R&C franchise (the fact that you made a point to say that is the only series that interests you makes me think you have already decided to go with the Xbox)----IMO there are at least 5 or 6 better Sony exclusives.... but again that's my opinion) I would suggest going with the Xbox.
Think what you'll be using it for most and which system is going to cost you more 1, 2 and 5 years from now.