You arleady said you are more into single player, so It seems PS3 is the likely choice for you. No need to pay for online you'll never make use of, and you still get access to all the DLC, though in some cases noteabley later then the 360 version, but you'll still get it.

And of course superior single player exlusives, like Valkeria for the SRPG fans, and Infamous for the action game fans.