First off, have the issues reappeared? If not, it seems like the driver for sure, and that's unfortunate given a LOT of people are using 500 series cards.
As for AMD and NVIDIA, on the hardware front I consider them about equal, although AMD's cards tend to get warmer (with the current-gen). Driver's wise, NVIDIA has been the superior.
Like most hardware, a lot of people are going to say they've been bit by AMD, and a lot of them will say they've been bit by NVIDIA. It's a luck of the draw, sometimes. When buying a GPU though, I always recommend going with one that has a nice cooler, because then heat shouldn't ever become an issue. But that of course relates not at all to your issue, which is driver-related. I was actually in contact with NVIDIA a couple of weeks ago about this, and the conversation kind of fell through. If the issue has kept at bay up to this point, you might want to try the latest 331.93 driver and see if the issue comes back or if it has been purged from the driver for good.
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<Toad772> I don't always drink alcohol, but when I do, I take it too far.