Which one do your kids’ friends have? If they’re all playing Call of Duty on the 360, maybe you want to go that way. Or run screaming from it, as the case may be.
If you must have Blu-ray, then I hesitantly recommend the PS3 (The online services suck somewhat less now). If you don’t care about Blu-ray, then the correct answer, really is “whatever your friends have” or, failing that “Whichever system has an exclusive or two that you want.”
I have an xbox 360, but i’d say PS3 to you. I prefer the 360’s controller, more mapped to my playing style but if you’re used to PS2 the controller is identical, same games plus, free online multiplayer.