I wouldn't be too sure about that. Those large map archives DO have loads of stuff, but...
- some tend to pack their maps in a very stupid way (like no folder structure)
- some don't include WADs, Overviews etc. (although available)
- some have broken/corrupt files
- some don't allow more'n 1 d/l thread (*hiss* *boooh!*)
- some spam you (like Filefront - *yuck*)
- and finally, some just don't have some maps, for no apparent reason!
The best choice is always the mapper's HP, IMHO. There you'll get a direct link to the archive, so that you can slap it into your D/L manager, and there you go.
If something can't be found on your US site, you can try:
www.clan00.de (German page, well-kept archive)
www.recoil.net.nz/files/category/30 (Kiwi site, as you can see - pretty good)
I cannot recommend cs.rin.ru. 2 of the 15-25 zips I got there were corrupt.