The nVidia drivers give better performance for the majority of games (due to both, games being developed using nVidia hardware, and better optimized drivers).
Still, the AMD open source drivers are becoming better every day, and meanwhile outperform the old AMD proprietary drivers in many places. Also, the open source AMD drivers are of relatively high quality (much, much better than the old proprietary AMD drivers).
As an open-source fan, I'd definitely go for AMD, but from a performance point of view nVidia seems to be the better option.
I also don't know about AMD GPU-Pro, as those drivers are specifically targeted at workstation environments, so I never bothered using them.