Well, Nvidia has the title of the worst driver bug in history at this point-
http://www.zdnet.com/blog/hardware/warning-nvidia-19675-drivers-can-kill-your-graphics-card/7551
So NV definitely cannot be superior to AMD drivers based on that fact alone..
That said, IMO I like both drivers. I've gotten BSODs with Nvidia drivers (verified because switching driver versions fixed the issue)- and never experienced that with my Radeons. But overall I wouldn't be scared enough of Nvidia drivers to switch back, I'm just in disagreement that Nvidia > AMD. I'd say AMD > Nvidia, even if just barely.
5-10 years ago I would've never come close to making this statement but a lot changes.