So I get an nvidia, and could do both. My conclusion? Nvidia is better on linux, so I use it.
Even TearFree video playback under compositing environment with nVidia proprietary drivers? Not likely. Even nVidia employees confirm that can not be TearFree (I would like to give proof-link, but nvnews forum is down).
AMD user here. i've had a laptop with an AMD graphics card or a long time. i haven't had huge stability issues. there were problems sometimes when suspend would cause blank screen on resume, for which a fix wasn't released for months. 2D is also worse than the open source driver. but, in general the driver is quite stable and 3D works amazingly well (infact, there was a huge boost in performance going from 11.8 to 12.3)
The blob has always been difficult to install for me but once it is I have had few problems. I did have tearing on one machine, but I also had the same thing when I tried the Nvidia blob with my onboard graphics card.
Regardless, I use the R600 Gallium3D driver on my main machine for desktop use and for gaming and find it to be the most stable of them all with the least issues. All it needs is better power management and faster 3D support, but both are certainly acceptable for me at the moment and can only really improve.
Though I will say I am impressed with the Intel shipped with my brother's Lenovoe 3000 N200. Not so happy with the one in our living room computer, but that thing is quite ancient.