If those are your criteria, I would go with AMD right now, because only the proprietary driver will get decent performance out of most nVidia cards. Nouveau is reverse-engineered and can’t tap into a lot of features of newer cards especially, and while I seem to recall there is a new open-source driver in the works, there’s no way it’s mature enough to be an option for anyone but testers.
I wouldn’t say the proprietary nvidia drivers are any worse than the open-source AMD drivers in terms of stability and performance (nouveau is far inferior to either). Their main issue is that they tend to be desupported long before the hardware breaks, leaving you with the choice of either nouveau or keeping an old kernel (and X version if using X—not sure how things work with Wayland) for compatibility with the old proprietary drivers.