Hey,
NVidia has superior DX11 drivers, which for your interests basically means you're losing performance on many modern games with an AMD GPU if your CPU isn't strong enough to avoid a CPU bottleneck.
Basically any AMD CPU is going to have this issue or Intel CPU older than an i5-2xxx though I'm speaking fairly roughly here as it varies by the game quite a bit for starters.
AMD has recently stepped up its game but NVidia is far better off financially and has been much better at keeping drivers up to date.
Basically, unless the AMD card seems really worth it go for the NVidia.
Other:
The GTX950 is far more power efficient than a similarly performing AMD card as well, but still make sure you support it (i.e. might need a 400W Power Supply or better with 6-pin PCIe connector or adapter).