The feature set is similar really... vBulletin appears to be from a UI point of view, a clone of UBB, with similar features and an almost identical design. However, vBulletin (and every other forum product I have seen) lacks the threaded/flat option on both the forum indexes and on post pages. Some have a mix of the two, but none do it as well as W3T.
I don't use any vBulletin forums frequently, but you should look at the display preferences here in your profile... I haven't seen a forum with more options to customize your viewing experience; from threaded/flat options, to style sheet choices, posts per page, e-mail notifications, etc.
Everything within W3T is very easy to use and works smoothly. I think a lot of that is thanks to the great support forum here, and most options are either thought up by the users here, or if not, feedback is given (and usually changes made) if a feature doesn't work properly/smoothly.
As far as speed goes, W3T is really quick. I use the PERL version and provided you have a server capable of handling your traffic, it will be very fast. So far I haven't ever visited a forum as fast as mine is now (on a dedicated server; not necessary unless you have a large user base and lots of traffic).
I always watch the new programs that come up, and some have some nice features, but none are dazzling enough to draw me away from W3T... in any price range.
_muhammad
:: imc_
