Stick with nVidia for their CUDA cores, although different software use CUDA and OpenGL/CL differently. If you are just learning, the the GTX 970 and up will do fine. If you are a professional, you may look into nVidia's professional lineup of GPUs including their workstation Teslas and Quadros. If you know your software uses OpenCL/GL more efficiently than CUDA, you can look into AMD's R9 380X, 390, 390X, and their Fury lineup. AMD also has professional grade FirePro cards that are similar to nVidia Quadros. After all, it all depends on your budget, purpose, and software.