ATI has driver issues, nVidia has driver issues. What's left?
I havn't had problems with nVidia's proprietary drivers. Many years ago, they used to crash my box repeatedly, but that all turned around in one release when they became very stable and still had excellent performance.
But as for what's left... there are several cards and chipsets out there that have opengl acceleration via MESA built into stock XF86/X.org distributions with standard linux kernels.... no additional downloads.
http://dri.freedesktop.org/wiki/Chipsets include many produced by ATI (including Radeons up to 9200), Matrox, almost all of Intel's chipsets, and 3dFX boards (Voodoo 3, 4, 5).
As for the performance, it would be good to get some feedback from others here. I've only tried to run my Voodoo 5 board with games under MESA-based DRI drivers. It worked, and had acceleration, but the performance was dissapointing compared to windows... That may not be the best comparison though, because the V5 in Linux could use only one of the two VSA1000 chips (essentially it ran as a V4). Also, MESA drivers for 3dFX cards worked by translating OpenGL into Glide, which probably also caused a performance hit. Stock 3dFX drivers for windows did the same thing, but the WickedGL 3rd party OpenGL ICD was available, and yielded a serious performance boost in Windows.
If you will permit me to opine momentarily, I really miss 3dFX.