As it is right now the GTX 600-series has all the newest Technologies (FXAA, TXAA, Boost). The AMD series doesn't have any of those. The GTX 660 also surpasses AMD 7850 in performance.
You can turn FXAA on in some games if you have an AMD Card, but Nvidia can in almost every game.
AMD can't support TXAA at all, it's a Nvidia thing - Just like physx.
The GTX 660 has boost, which Means it overclocks itself. I got the GTX 660 and when gaming it goes from 980 mHz to 1110.5 MHz.
The performance of the GTX 660 is on par with 7870 and GTX 580.
I would recommend the reference cooling design by Nvidia. It will have decent temperatures in every Tower. While other cooling solutions will be bad in some cases.
1. AMD 7850 is better performing than the 660
2. AMD can use physx
3. AMD cards can be overclocked in CCC
4. the GTX660 is on par with the 7850 and the 660ti is on par with the 7870