MyBB's actually the only forum software I've never tried. I like the Simple Machines one, but it was just hard for me to make themes for it. XMB annoyed me, it lacked in the admin department. >_> phpBB's the very first forum I've ever used, and I got the hang of it right away. But, yeah, like you said their admin CP is very confusing. I wanted to make a usergroup for Moderators (which I can't believe they don't have, either @_@), and their permissions kept bothering me. >.<
EDIT: I just checked out MyBB. I'm kind of in love with it. =)