DX is marginally better for crappy cards like Matrox and Intel. Manufacturers that produce high-end OpenGL cards (like Wildcat, FireGL and Quadro) will have optimised OpenGL drivers for their cards.
Well since you've ignored the two most popular ranges of consumer-level cards entirely, I'd have to say that many, many more of my customers are using Intel than are using Wildcat, FireGL and Quadro put together.