I'm rather specific in where I choose to buy my games, and have a Priority system:
1st Priority: Buy Game New from Willow Video (A local to my area gaming store)
2nd Priority: Buy Game used from Willow Video. (I'm probably there looking for the new copy already)
3rd Priority: Buy Game New from Anywhere I can find it.
Final Priority: Buy Game used from EB.
I prefer to get my games new personally. First off, you know the condition it's going to be in, I'm kind of anal and like my things in near perfect condition. Second, you know where most of that money is going, the Publishers for the games, and I like to know who's pocket my money is going into when I buy something. I support Publishers of games I love by buying their games new. Finally, sometimes new copies come with codes for free access to online servers and DLC etc.
If I can't find a game new, and it's for sale Used from Willow, I buy it. I do that because I've been shopping there since I was a little kid, it's a local business that doesn't really spread outside of this area, and I like local business. If I can't buy direct from the publishers, I really don't mind buying from Willow. They are very reasonable in how much they purchase used games for from customers, and their used game prices are also reasonable when selling back to customers, at the very least always lower than EB games. Just the other day, I needed a Mic for my PS3 for Rock Band. EB wanted to sell it for 35 bucks, and Willow had one for 10 bucks new.
On the topic of EB games, I avoid shopping there whenever I can, and I try to ONLY buy new games there, never used. Their used game market is terrible, they pay next to nothing to acquire the games that they do, and then price gouge as much as possible. Buying new from them isn't terrible, because like 90% of that price goes to the Publisher anyway, but a used game is 100% profit for them... and I could have bought the same game from Willow, a company I LIKE, for cheaper. As such, I do not support EB games used game market both by not selling to or buying from, them. On the rare rare rare occasion they have a used game Willow doesn't, I'll buy it, because in the end, if I want a game, I'm going to buy it.