Personally I prefer phpBB. Why? It's easy to use, much more so than IPB in my opinion. It also doesn't try to leap out of my screen and make dinner for me as well as do the washing up.
The thing is though, you cannot choose your own favourite forum board based on our opinions or our thoughts. Each person is very different, and while some people will want one thing, the other person will want another.
The best way to find out which is best
is to try them all out and see for yourself.