XF works as promised, vB does not.
XF is a breeze to install and upgrade, vB is a nightmare.
XF updates solve bugs and/or introduce new features requested by the community. vB introduces new bugs, and features nobody requested but that make IB a few bucks in affiliate programs.
If you are new to forums and this is for a new forum that doesn't currently exist, then just go with Xenforo. You won't be missing features you don't know about and your users will have no prior experience with your forum and thus they too will not be missing anything.
If you are serious about the forum, as in you have a business and a marketing plan for it and it can realistically become a revenue generating site, then I'd suggest to buy the three viable commercial scripts (IPB, vB, XF) and thoroughly test out which one fits your needs the best at this time without consideration what may or may not happen in the future. I'd make that choice based on logic and rationale rather than on emotion.
Xenforo is faster, and a better user experience than vB.
I found vBulletin harder to administrate as well ... so many million features - it was overwhelming.
vB was great software.
was. The vBulletin 3.x series will go down as the golden age of forums.
vB4 was a total disaster, and still is. vBulletin 4 is almost usable now, if your standards are low.
I didn't want to leave vBulletin, but I couldn't pick inferior software either. Now that vBulletin is run by a large American Corporation it performs and feels like a bloated mess.
Xenforo is missing some things that super picky and experienced admins want: Ignore features, thread prefixes, and a robust gallery. Those things will be relatively easy to fix. Fixing the utter mess that is vBulletin 4 might prove impossible.
If you give details of your plans, I would give you an honest opinion of whether or not vBulletin or Xenforo is better.
I built many projects on vBulletin's framework. The procedural style code that was employed made for a more difficult time creating some of these. XenForo's framework was more thought out (in a time when you had "frameworks") and much easier to extend. I thoroughly enjoy my projects on XenForo and have plans for quite a bit more in the future.