It is unfortunate that Hammer can't be used for Quake maps according to the license agreement because Worldcraft 3.3 messes up texture alignment with the import of standard [non .map 220 format] Quake .map files where Hammer 3.4/3.5 imports them just fine without any problems.
Worldcraft 1.6 is nice but lacks OpenGL acceleration and cannot maintain texture alignment with rotation. Plus I think the standard download is just shareware, I can't remember the unwanted limitation imposed with the shareware version.
Worldcraft 3.3 and Hammer 3.4/3.5 do not have a way to brighten the 3d textured viewed which it seems is too dark on a lot of people's computers (this can be worked around using the setgamma.exe [ that can be downloaded at the DarkPlaces site among other places]utility to artificially brighten it ).
It seems that common consensus is that Radiant is hard to work with for many people because it can't do the 4 screen view many people are accustomed to working with.
The BSP editor that some people rave about is closed source, which like Worldcraft, is just another way of shooting yourself in the head ... if not today, then tomorrow.
A few people like Quark. I personally couldn't figure it out and it seemed hard to use but I also didn't give it a chance, but I heard it can have "issues".
This project IS open source, QuakeEd (
http://www.celephais.net/board/view_thr ... &start=142 ) and some people think it has a lot of potential. As I understand it, initial setup is confusing and lacks a nice screenshot to help someone set it up. It is my understanding that it lacks keeping textures aligned with rotation, but maybe that will eventually happen.