Well, I'd suggest from a store because it comes with a CD. If you really care about it, use the CD to install it into your hard drive. But, you will need the CD for verification to play the game. Also, what happens if something happened to your Xbox LIVE account, I'm not sure, but I think you won't be able to download it if you happen to get banned. Just by a used COD 4 game, there is pretty much no difference to a new one. I got a used one at PlayNTrade for 10$.