I would go with the GTX 950 if you prefer Nvidia card as it is in Benchmarks i have seen a better performer. Also Nvidia Graphic Cards are more supported in todays Gaming Scene due to the special ingame feautures it provides. And the fact you like the PhysX is a other reason to go with the GTX 950 instead of the r370.
Personally i would go with an AMD r380 which out performs the GTX 950 and cost nearly as much as the GTX 950 so keep that in mind. It got a stronger core than the one in the GTX 950 with the same amount of VRAM and it Benchmarks proven that you will have more FPS than with the 950