Take the following into consideration:
Both
UBBT and vB have a UBB-ish skin, downloadable from their forums (threadsdev and vb.com).
UBBT has many users from here, such as Allen. Many
vB threads bash UBB because we're using flat files, and usually vB.com/org admins join the bashing.
vBulletin has some (more than 1) hacks that you gotta PAY to use, while in UBBThreads everything is free, however UBBT doesn't have these hacks that you gotta pay for in vB. Many databases crashed from
vB, while UBBT had only single cases of crashing dbs.
UBBT has 24/7/365(366 once per 4 years) support, including chat in the mornings and afternoons.
vB has a
bigger database of hacks
and users.
Not bashing, just stating the facts and rumors.