Re: What is the biggest forum on bbPress?
Also, a plus for bbPress is that it has built-in user integration with WordPress – which as far as I know doesn’t exist on any other platform.
If you have the coding resources in-house and are familiar with WordPress development, I think you will find bbPress quite comfortable and flexible. However, in it’s current alpha state, bbPress is not for the faint of heart, there are known bugs and missing functionality in the current releases. But if you have people willing to fix them, submitted patches will be in core before you know it.