Once I used phpBB forum, but eventually changed the engine due to the large quantity of spam user registrations.
I find Simple Machines forum http://www.simplemachines.org/ much more comfortable, convenient, customizable and spam-protected.
See the comparison at:
http://kb.siteground.com/article/Forum_ ... s_SMF.html
http://www.forummatrix.org/compare/bbPr ... +vBulletin
http://www.theadminzone.com/forums/show ... hp?t=16952
It's relatively easy to convert the forum to SMF.