As Ashley said it's really what forum software you like and are most comfortable with.
If you've got the extra cash, my best advice would be to get a paid hosting plan and host phpBB on it, then you can have full access to it and not have to worry about being limited in your forum's features.
For example, I chose PHPBB as the boards I have signed up with over the course of the three years I've been foruming in general (with a few exceptions) have all been either on PHPBB2 or PHPBB3. This is the exact reason why I chose to go back to PHPBB, because I was familiar with the ACP (although the forum permissions and stuff are kind of confusing) plus I'm accustomed to the posting interface and things like that. That's why I've chosen what I chose.