8800 GT>HD 4850>HD 6950> HD 7950> Xfire
The only card that died on me was a PNY 8800 GT XLR or something like that. It performed superb while it lasted(2,5 years). I changed sides to ATI/AMD and so far so good, very happy with all of them, 3 Sapphire cards always overclocked mining bitcoin all day on air, I traded my 6950 for a faulty ASUS 7950 DCUII(1st batch got heatsink problems) changed the heatsink to an Arctic xtreme and xfire it with a sapphire 7950 dual x. Maxing every game so far(my monitor is 1080p lol).
I keep an open mind so I could change again if Nvidia offers a good performance/value card but for the time being AMD offers the better deals on my budget segment.
Note: I never had driver issues with any of my cards, not even on Xfire, I just wait for stable releases and only go beta if the performance gain is very good(not very often usually)