Wow, that's a tough one! Amazon's sales were good, but I also got a bunch of stuff off Steam... But I think not being able to get Left 4 Dead at Amazon puts Steam over the top.
Although amazon had some great deals, I only bit for The Orange Box one. However, I nabbed quite a few good deals at Gamefly in that period, and all in good condition, so that gets my vote.
It's a tough choice. I got some great Black Friday deals from Amazon, the Steam deals were great too, and I got a much cheaper PS3 due to Live Cashback. I think I am going with Amazon on this one though.