Bob,
I don't have any direct experience with phpBB myself, however I do know from experience from the Service Desk that at times phpBB has had it's share, maybe more than it's share, of bugs in the past...
I have not seen anything that changes my opinion from 2010...
http://www.aota.net/forums/showthread.php?t=25334
VBulletin still seems to be the Gold Standard however the changes in VBulletin 4.x seems to have alienated some users and SMF (Simple Machines Forums) seems to be gaining traction (it's cost is far better than VBulletin, FREE) and I have seen some very large and busy Forums running on SMF successfully...
Just my two cents of course
(adjusted for inflation probably worth $0.001 today LOL)
-Bob