Just watched a video comparing all the different places to preorder from. If you're gonna defect from BARFtron and get BF3 on PC, order it from Origin (EA's in-house store) so you get early access to the Beta.
If you're Xbox, then pre order from Origin or Gamestop. Only those two come with the Karkhand map/weapon pack, which you get with a pre order from pretty much everyone...but they also come with a Physical Warfare pack. Type 88 LMG, DAO shotgun, flechette ammo, and a flash suppressor.
Best Buy pre order doesn't get you the physical warfare pack, but you get alternate skins for each class.
I'd rather have more guns and equipment from the start than extra camos. So I'm glad I already have my pre order at Gamestop.
Pre order for MW3 on the other hand....fuck it. Wherever you want. They've never given much if any in game content for COD pre orders. Last thing was a pilot suit thing for your Xbox live avatar with the Black Ops pre order.