If your simply building a straight up community then VBulletin hands down even at it's current price is the best IMO. However as already stated, there are many factors that come into play. What type of project, your programming experience, are you wrapping it / integrating it into your current site, etc. If you are experienced in php and want complete control of your BB software and wish to integrate your own coding into it then IMO SMF is the way to go. MyBB is a good starter BB for those without a budget. However with all that said, IPB has been climbing the ladder with the past few releases and the primary thing they have going for them at this point is that IPB is completely tableless. Something with VBulletin lacks so far.
I think phpbb is good enough and free! that's what I'm using for a couple of forums I think is a lot better than Vbulettin I don;t know why people like to stick to it
I use vBulletin. I think its probably the best. However there are alot of reasons why its a bad script.
I don't think vBulletin is the best any day. I have looked at how it is made and there are MANY outdated ways of handling stuff and MANY things that makes it slower than modern forum system. I cannot recommend it. I do however think that IPB recently got a makeover that makes it much faster. That's all I know.