I've actually played around with wwwthread, ultraboard (the old version when it was free). I found (solely my opinion) ultraboard to be more or less a UBB clone.
I agree WWWthread is the best board around, and yes it's free. But it's such a pain in the ass to install, and although it's not user-hostile it's not user-friendly either. If I do decide to switch to another board, expect it to be phpBB
