To get the $20 in reward certificates from Best Buy, you need to be a Gamers Club Unlocked member, which costs $14.99 a year. So, unless you're already an Unlocked member, Amazon still offers the better pre-order deal.
Yeah, if you're just talking about one game, sure, Amazon has the better deal. But if you buy even a few games per year, the Gamer Reward Zone is the better deal, hands down. I just got it over the summer and made my money back on the first magazine I got in the mail. I'll be using the gift card from this towards AC3 and so on, plus bonus reward zone points between membership and the CC.