It all depends on your budget. I really do prefer ATI, but I use a Matrox G400 (single) and it gets along fine. Since the original games were pretty low- res anyways, the only reason you may want a to go with a higher resolution would be if you wante clarity beyond the original game with the rendering. I suppose this is technically possible (as I've done it in Zinc) but it's not faithful to the original. Matrox G400 have the power to push most arcade and console games I know of at 640X480. They probably wouldn't be the first choice for PC games since they're old news now, but they handle emulation pretty darn well, they're solid as hell, and they've proven themselves on the emulation scene.
I actually showed up at a friend's house to play Quake 3 with him and I took computer. He was like "what the heel is that thing" but it kept up pretty well throughtout the whole game. Maybe it didn't get 100fps but it got 60 fps.
Granted a newer ATI is better, but my Matrox G400 is "good enough" and you can find them in AGP or PCI. For people with other stuff to be spending their money on, I really think a Matrox can do the job.