Gamestop - I like the store just fine, and the web site is great for looking up stock at the B&M stores. But the last things I ordered online were refurbished pieces o' crap so I've pretty much stopped buying used games. They are decent enough for buying new stuff, though, if you have credit to burn from their great in-store trade-in deals.
Personally, I'd like to give GS the award for best B&M store and worst online store but they didn't make the best store nominations. I know a lot of CAGs will vote them worst B&M store but I just can't do that given the trade-in deals, easy to find stock (using the web site), and numerous convenient locations.