As far as having the amount that DP has, and the topics they have active discussions open in, I'd say no one.
http://www.sitepoint.com - That's bigger. Its not that wise to use just one webmaster forum though, You should widen your horizons
wow the KC chiefs is right above ya I'll have to check that one out, see who all is bashing t-green..lol btw, I bet the 611 isn't true,, there are some big boards not listed at bb