I've had a Creative Labs GTS, a Guillemot Prophet GTS and an Inno3d GTS
The Inno3d has significantly better 2d quality, and is faster.
Of course, it's a GTS Pro, so that explains why, but I would say not to worry about the quality of the Inno3d, as it is every bit as good if not better than the 2 "big names" I have tried.