[xdude]

This is a common question in web master forum and it's kinda a question all forums have. If this question was asked 5-6 years ago I would say it's SMF but now I'm a big fan of myBB. Main reason is it's lot easy to deal with core and plugins unlike in SMF. Also myBB has lots of nice plugins which are easy to install. Only downsize I have seen in myBB is lack of really nice free themes.

I tried to used phpBB long time ago but I had kinda too many problems while trying to install and also I was told too many people it has lots of security problems.