I have the GTX 670 you're looking at. Fast and quiet. At that resolution, you won't have any problems.
From what I gather, you'll get the same results qualitatively with the AMD. Choose whichever you prefer, be it price or nvidia/amd preference.
you can't go wrong with either, but a top class card like the vapor-x costs what's equivalent to $100 less than a decent 670 here in Denmark.. makes it easy here