"NVidia cards are stable but bad image quality in all OS."
I'm sorry, but that is a ridiculous statement. "bad image quality" is wrong, just plain wrong.
2d image quality? Okay, it's pretty bad, but it's 3d image quality is excellent. It's 16-bit isn't as good as 3dfx's, and its 32-bit isn't quite as good as the Radeon's, but it still has excellent image quality.
Let's be real here people, all 3 of the "big 3" are excellent cards. Each has its own strengths and weaknesses, but each "weakness" is only relative to its competitors, not overall.