PHPBB was ok, but it had very bad security. SMF is one of the most secure boards, and we have had very little trouble with it. It's also easier to update and manage. The only thing that made phpbb better was that people could request membership to user groups by clicking a button, now they have to pm the group leader.
I don't know about the new versions of PHPBB though.
There is also one other board that's considered to be good, invision power board, but it isn't freeware.