GTX660 is comfortably in the lead. It also gives you adaptive v-sync, meaning that if you use v-sync to prevent tearing, it'll switch off when your framerate drops below your refresh rate (typically 60) rather than restrict your framerate like standard v-sync. In summary, you'll get better framerates anyway, and much better framerates still below 60fps using v-sync.
But! These benchmarks were done after AMD's major new driver release, but before nVidia's big release, giving AMD the advantage. nVidia's new drivers are adding between 5% and 20%. And like Lostgamer_03 says, adaptive v-sync ;-)