personally I dont know which one is the best but I do know of 3 Subforum mods only:
Category Hierachy Mod
Simple Subforum Mod
Subforum Plus Mod
I havent tried Ch Mod yet, but I am trying Subforum plus mod, which is still in development, however, it is working fine accept for the mod I wish to have it working with. I hope it will be fixed very soon.
If you install CH on an existing Mod, you need to watch out for existing mods on your current forum, since there might be some incapabilities.
nevertheless, please do the search for the 3 mods I listed. Other users experience something different.