A question for those who own both Ps3 and xbox 360

I got a question for the folks who own both playstation 3 and xbox 360: when a game is released for both platforms, and by the reviews there's no difference between the two versions, which one do you buy?

If the game has multiplayer, I buy the ps3 version because most of my friends have the ps3 and if the game is only single player I get the xbox version.