The Mingle Forum plugin seems to offer a decent set of features and I would like to use it, but there is a conflict between Mingle Forums and Jetpack's Share module that causes the forums to display multiple times on a single page. This is a deal breaker for me as I need my twitter sharing. If not for this, I'd give Mingle a 4 or 5 star rating.
The author claims it's the fault of Jetpack and there is nothing he can do about it, but Simple Press doesn't have this issue. I am not sure what the reality of the situation is. Regardless, if you don't need to use JetPack then Mingle seems to be a good forum plugin. If you do, then you should probably look elsewhere for your forums solution. (And don't do Simple Press unless you are willing to fork out some cash for support.)