Well, some claim that ATI has better image and Anisotropic Filtering than nVidia. So does that mean that their better than Matrox? Hm... Looks like you would have to do a comparison between Matrox and nVidia for that one!
Absolutley Matrox.
Best clarity.
Untouchable color saturation.
And with Parhelia and P-series cards, 10bit gigacolor nobody else even offers, plus Glyph Anti-aliasing.