But i've seen vBulletins code, the code that handles mySQL, its not very well balanced.
I am NOT bias, if i liked vB better than UBB i'd tell you such. But i dislike vB which includes every reason LK states (not to mention vB.org using a style inwhich Cal created for ubbhackers without crediting cal). So, tweak ubb.classic, use ubb.threads (import is smooth as a babies bottom).