Which drivers would be better to use if someone is using applications for Image and Video Editing (like GIMP, Inkscape, OpenShot, Cinelerra, PiTiVi, KdenLive, Avidemux, Kino, Lives and others) in matter of performance and quality: AMD Radeon Open Source driver or ATI/AMD Proprietary drivers?
The propriatary drivers are normally a lot faster than the Open Source ones in 3D acceleration so I would figure that the impact will depend on the software. If the video or photo editor uses 3D acceleration then you will notice a difference. For everything else not so much, the 2D performance of the open source drivers is pretty good.
There should not be any performance differences when you install software drivers via the Additional Software Drivers tool that comes built in with Ubuntu.
That is the recommended way to install drivers and it is how I personally install drivers, such as those for my video card, which is an ATI Radeon 5450.
I don't know if the drivers installed via said tool are different from those installable for windows but I actually have better performance and less hardware usage in Ubuntu compared to windows. I've edited images in GIMP as well as edited videos on both Ubuntu and Windows.
Simply put install your drivers via the Additional Software drivers and you should have no performance issues.