Well, as I'm sure you know already, phpBB is free and vBulletin has a pricetag of $160. vB has much cleaner code. It also has virtually no bugs, and when one does arise, it is fixed within the day. It comes with many more options configurable via the admin panel. In addition, their templating system is amazing - especially template conditionals. All I could really suggest is going to vBulletin.com and testing out the demo admin interface to see just how configurable it is.
I like both to tell ya the truth, however Dani is right, it IS much cleaner and more enhancments then phpBB. Again shes also right as well on teh Price tag. It is pretty expesive for a piece of software. IPB is clean too, but very similar to vB though.