Tenebrae Is Rarely Used I Woul;d Say. Its Pretty Buggy To Be Honest.
Darkplaces is the way to go if you want uber-eyecandy.
You need to download one of Rygels hir-res texture packs though. The texture pack is installed in id1\textures, and contains all of the actual bump-map files as well as the textures.
Most mappers use FitzQuake because it is fairly true to the original Quake in look and feel, and considered to be sufficiently stable for pretty much anything. It also support colored lighting and external hi-res textures, in the same way but doesnt support all of the normal-maps files and bump-map information files and shit like Darkplaces does. I use FitzQuake.
AguirRe's Modified GLQuake used to be the standard for map which are too big for the standard Quake engile limits, and his engine supports many superb features for the mapper, like leak detection and enhanced bug reports.
Telejano is a cool engine :) I dont think so many people still use it really, but I liked it.
You should google "darkplaces quake" and you''l find lordahvocs webpage for his engine, there are loads of links there. Alternatively there are links at http://www.quakeone.com\