Not sure if its been mentioned as of yet, just gingerly scanned the prior posts;
I've used most forum software out there, they all have their pros and cons. But it seems most of the people on here only care about customization over stability.
IPB: Really nice and flexible, pretty customizable, *nicer* looking than older VB.
VB: Ideal for most communities, highly customizable especially in the 3.8 versions. Newer versions look nicer but you can change just about everything.
XenForo: Just started using it, liking it a lot.