i would like to point out that MYBB is free and "OPEN SOURCE"
wich means that would have more vulnerabilities than other paid forum softwares
i must say that is the best for me,. why??
its free and easy costumizable and the community its growing each day giving more resources (free) and also tech support
ive started desiging in IPB 2.1 and it was hard but still ive managed ok, but in mybb easy as it can get