IPB, vB and phpBB are all good in their own respects but I think IPB is the best. The Admin CP gives you so much depth and control over the board, the forum software is easy to navigate etc. and its expandability with all the mods and skins being made for it etc. make it the ideal forum software. Lots of versatility and room for being creative with how you want to set it up
IPB is nice and also Invision. There is an other one with some really good features but I forget the name .
i always have used phpBB. there are security mods you can put on it to make it more secure and you can also add an arcade ^^. the mod is somewhere if i find it i will post the link.
I would have to say PHPbb is my favorite. Although, client side I would go with IPB. PHPbb is really great, just don't get version 2.0.1 because I've had problems with that. Someone who I share a website with, screwed up our brand-new PHPbb 2.0.3 forums by trying to fuse it together with our crappy 2.0.1 which had this ----ty error almost everytime you posted or something