I have tried MyBB
I have tried phpbb
I have tried SMF
I have tried vBulletin.

For me i find vBulletin to be the best by a long shot.
MyBB second only because of usability. Hate the community forums and the staff over there.
The rest dont matter.
Although vB is harder to use than some it does have a very powerful backend IMHO. No end of admin options.
Loads of mods for it and nearly all free (paid versions as well). Good mod support on there .org domain.
A great updater which i simply cant fault. Making upgrades a breeze.
I do find vB has a limited selection of themes though.
But vB has a cool theme creation tool built in that does work all be it in a simple fashion.