SMF 
I liked VBulletin because it is a semi-standard out there across professional websites, however – I don’t care to pay for it. PLUS – I did use it once for one of my websites (as a leased license) and after the lease ended and I forgot about it – they went in and removed ALL my database. Which means all posts and content were stolen. I’ll never use them again.
phpBB is ok, but I think that the SMF guys are more pro-active on updates to the software and there are a shit-ton of mods ready to use for it.