I am going to go for PHPbb (Temi knew I would )
My forum runs on it and I ahve had absolutely no problems. Then again I pay a dude to handle all the modifications I want, ahve had a back end admin panel re0write, and LOTS of custom changes.
I might end up changing to phpbb3 (just released) then again I might not. I have around 420,000 posts on there and it runs like a dream!