First the non-SDL version: As far as I can tell, this version is completely stable, and there are no graphics glitches long as one does not turn on OGL2 -in which case all manners of odd things pop up on the screen. The big downside to the non-SDL version is the sluggish mouse. The menus are painful to use when it takes several full sweeps of the arm to move the cursor anywhere on the screen. The in-game mouse is likewise sluggish - even when the sensitivity is set to max. Not only it is slow, but the game seems to lag behind the mouse movements. As far as I can tell, the only downside to the non-SDL version is the sluggish mouse. OGL2 I can live without.
The the SDL version: First, it seems as if the drivers corrupt the textures in the VRAM, which results in non-rendered sides / missing walls, garbled textures, semi-transparency where there should be none, and other oddities. These effects can be circumvented to some degree by using gl_picmip.
However, the SDL version seems to be degrading somehow. gl_picmip no longer works as as well as it did when I first started using it, and is sometimes makes Nex crash. SDL Nex often crashes / freezes when changing levels.
And a new symptom that has appeared in the past few days is that the HUD no longer renders properly. All I get is a mess of pixels. I was able to get rid of this symptom by going through the gl_picmip routine, but no longer. I can no longer see how my health, armor, and ammo is doing. I don't understand how software like this can degrade over time like the SDL version seems to be doing. There's nothing strange going on in the config file either.
Still, if it was possible to make the mouse in the non-SDL version snappier and non-laggy, then I'd happily use that one instead.
See below for system specs.