Gamestop, Toys r US, walmart, best buy or Target, whoever is running the best deal. If they are all the same i would go in that order.
My main place is Amazon, I wait for a good sale before I buy any game. I do buy games off the PSN store but when it is extremely discounted and Gamestop is my last place I shop, I only go there when I buy a game at midnight other then that I avoid Gamestop if I can.
I find it odd that in America GameStop seems like a monopoly ( I know it's not the only place that sells (physical) video games, but it seems to be the only actual video game store in the country.)
I buy my games from different online video game stores.
"How do you prove that you exist...? Maybe we don't exist..."