That should be a question that only you can answer because you know which requirements are important for you/your clients.
I've used vBulletin for almost a decade and never had problems. However, it's not so much the quality of the software than the popularity and features that made me choose vBulletin over others. I had used others, by the way like SMF's predecessor (YaBB - anyone remember that one?) and phpBB.
If I were to look for feature-rich forum software to use today, I'd look into vBulletin (haven't tried the new version), phpBB as well as IPB. Otherwise I'd use something like Vanilla or punBB, both extreme light-weight forum applications written in PHP.
In other words, if MyBB does everything you need, I'd give it a try.