I think the amount of VRAM is more important than whether it’s an AMD or Nvidia chipset - especially if you plan to use a VR headset. I bought a 3090 Ti because it has 24GB VRAM. I don’t want to be lacking in that area. I think 12GB is the minimum for non-VR use if you’re buying a new card today, and 18GB is minimum for VR.
(Standing by for "YOU’RE WRONG! I RUN VR ON MY FX5600 WITH 2GB VRAM JUST FINE!) 
Also, whether your monitor is G-Sync or FreeSync compatible.
G-Sync works with nVidia cards.
FreeSync works on all AMD cards and some Nvidia cards, too. But there’s a catch — it’s only guaranteed to work correctly on FreeSync monitors that are certified Nvidia G-Sync Compatible.