Didn't know that Mybb was a common used forum software. I compared the software packets when I chose mine. I chose Mybb because it's free and there are many plugins available. I installed many themes on mine but I'm still not sure which theme appeals the most for my forum. Did you test them already ?
I'm probably mistaken, the reviews I was thinking of were talking about phpBB. I thought MyBB was a newer version of that, but that's obviously not the case.
http://www.webhostingshow.com/2010/04/02/comparing-the-best-free-forum-scripts/http://www.techsupportalert.com/best-free-website-forum-software.htmI prefered SMF from the beginning, both because I like its functionality better than phpBB and because I'm used to it from being a mod on ASN, so when I saw it was consistently in the top 3, I didn't hesitate. As for the themes, I went throught the entire collection, tried about 20-30 of them (most were immediately discarded due to defects), and then kept the one I liked most with the second and third as alternate choices for users who prefer to pick another theme for themselves. I might be adding more options if people ask, but I probaly won't be changing the main theme anytime soon, because I really like it.

(It would be even better thought if the blue curls had the shape of Blue Exorcist flames. If there's anyone who can do that...)
EDIT:
Well, whadda you know. Now a new member showed up in the list, but not in the stats. Apparently there's a bit of a delay (probably until they have confirmed their registration).