I do not know anything about wordpress forums but there are things that bother me witg xenforo
0. No good system for admin permissions, becuase of that i end up having to limit the mod accounts more than really necessary.
1. you cannot properly make email optional, current solution is to have confirmation be optional so you can enter firstname.lastname@example.org (doesn't exist) or something.
2. messy and confusing settings (admin control panel)
3. limited media upload options.