I've only used their customer support once for a question, but it wasn't that great. It took them a couple days to a week to respond to my replies. This was most likely just an isolated case, though, as I've heard a lot of good things about XFX support.
(A little off-topic: best support I've used was NCSoft's. I got detailed replies within an hour of my replies).
I'd go with ASUS/XFX/ZOTAC if you ever plan on selling your cards. I'm going to avoid evga and bfg because of their horrible warranty policy (only extends to the original purchaser).
Guess what EVGA/BFG, let's say someone sells their EVGA card, and it eventually fails on the person who bought it, so that means you guys will refuse warranty. Guess what? It would have failed either way, most likely, if the original owner kept it, so you'd be stuck replacing it anyhow. It's not like you guys are losing anything. At the least, stand by your products. I'll basically never buy EVGA/BFG because of that.
XFX customer support was good for me the time I've delt with them. I had a bad mobo and sent it in. I called them and explained "I've done this, this and this to trouble shoot". They said, "That's what we would of told you to do so we'll send you a new one." It was that easy. They sent me a brand new retail boxed replacement. Was nice to have twice the accessories