I use a lot of openbsd and you won't be running nvidea drivers on openbsd for love or money. there is nouveau and they are doing amazing work, however, they are also up against a petty, secretive company that appears to hate them. So nvidea is out.
Understandably openbsd gets zero support from the manufactures. So we need an opensource driver and some brave heroic soul to volunteer their time to get it running.
AMD drivers worked well enough and if you want decent 3d acceleration the only real choice. However they tended to crash and 3d acceleration is usually not a priority if using openbsd. Also starting with amdgpu the drivers got big, really big. The amdgpu driver nearly has more code then the rest of the openbsd kernel[1]. it is this big mess of generated code where each card uses a slightly different ISA. I understand why having a stable ISA is not a priority for AMD(it lets them change the card architecture easier) however sometimes i wish it were documented and pinned down. it would certainly make for a more stable driver that is easier to integrate.
And then there is intel, Note that I have not used intel graphics since 2016 so my experience is out of date. but once you got past the first generation of intel graphics the experience was rock solid, the drivers always worked well for me. if asked for the best openbsd experience I would recommend intel every time. However my last few machines have been amd and unfortunately there is no intel graphics add-in card(i looked). My last intel box I had an amd 3d card but I only used it under windows to play games. for work/openbsd I would just use the onboard intel graphics as they were more stable.