Neither one is great although I heard that AMD uses sleeve bearing fans for their reference while nvidia uses ball bearing which gives nvidia an edge IMO. I wish nvidia didn't use an heatspreader because I've heard they use non-AC MX2 under the IHS in addition to using non-AC MX2 over it. Even though it's only the top, I still I remove the stock TIM from the top of the IHS, "purify" the surface of it, and put AC MX-2 on it.
I've always had good luck with eVGA's customer service, although I have always bought their cross shipping plan. My eVGA GTX560 Ti 2GB hasn't had any hardware problems, although I haven't gamed with it a whole lot and I have it undervolted and underclocked anyway. I have an Asus (reference) GTX 460 768 MB that I haven't used in 6 months or so, but I didn't sell it because the BIOS was write protected. I didn't have any issues with it other than that it doesn't display anything via DVI until Windows was booted into (which was why I tried to flash the BIOS)