I just gotta say, if you ever preorder ONCE, then it essentially has paid for itself at bestbuy... Know how much I paid for Dead Island Riptide? $15.94 (used a previous $20 RZ Cert, and had pricematched newegg when they had the preorder at $35 (another great benefit, although now pricematching has to be done at the time of the purchase...). It's always useful when a different place is having a sale, like say amazon, but instead of waiting a couple day's you could always walk right into a bestbuy, price match the item, and walk out with the game, 40 minutes later of course after they finally manage to do it on their crazy slow system's...
Bestbuy IS good for trading in games (nice little trade in value list on their site) Plus you can get a gift card that's good for anything.
So, my two cent's would be Gamestop for used games (they generally have a better selection, and best buy you cant examine them first.
It's a toss up between the two for Trade in's, Best buy you can see what each game will get you, and many newer game's will get you a very good amount but gamestop offer's better deal's on older but still popular game's, and with some promo's offer you more than the game really should be worth.
Although new game's and (In the past, Pre-order's for a few of the bigger title's) are better to get at bestbuy, you can pricematch, so any sale from anywhere is essentially a sale at bestbuy, also their coupon's are better (YES I KNOW, not as good as they used to be) but heck atleast the magazine is of SOME value!