XenForo License $140*
Includes 12 months of ticket support and upgrades. Support and upgrade access can currently be extended for $40 for an additional 12 months (see details). Bulk discounts are also available.
I can tell you one aspect that is not secure in vBulletin compared to Xenforo. It's the add ons. Add ons cause security flaws in vBulletin, i know this to be 100% correct because my vBulletin forum was hacked through an add on. I will not go into it because it's ancient history now but Xenforo is indeed more secure.