If you thought architecture for CPU's was important, then GPU architectures are magnitudes more important.
Newer architechtures for GPUs are better.
For NVidia, its Maxwell 2.0 (9xx cards) and for AMD, its GCN 3.0(I'm pretty sure)(3xx series).
Technically, Maxwell 2.0 is more advanced, but AMD used its GCN 3.0 architecture form the 2xx card series and piled on more transistors, and sells the cards at the same price point as NVidia for close performance. NVidia has better drivers, and AMD has better compute performance, but the performance is based on the price point mostly.
While choosing GPU's, look at how each GPU in you price range performs in which games you want to play, and buy the one that gives you the most FPS for your money.
Also consider other things, such as G-Sync, Freesync, NVidia has Shadowplay and AMD has something that I cannot remember competing with Shadowplay, NVidia has CUDA(But I don't think it matters to you)