I'm currently reviewing vBulletin for use as the main TOE forum. From what I can tell so far, it looks like it has more to offer, promotes a better user community, is easier to manage, and has better support. If you go with vBulletin, I'll make the change before the end of the year and all posts and user accounts would be ported to the new system.
If you want to weigh in you can post a comment or answer the poll. You can check it out yourself
here.