I can say the exactly the same as Zell, point by point.
I don't have an AMD card so I can't speak by experience, but by the feedback I got, AMD should work fine if you explicitly select D3D12 for output API.
Aside from performance, even Intel HD Graphics seems to work as expected, both with D3D11 and 12.
That texture issue with D3D11 is very annoying though, I always get a report about that. I don't know if the upcoming series will behave the same (or it needs different driver internals and we have a chance).
As far as support which one has provided better support as far as fixing bugs in their drivers or feature levels?
I don't know. I only submitted reports to AMD, but honestly and not surprisingly, I feel that's equivalent to submitting reports into /dev/null. 😁