I've been using vbulletin on forums for almost 10 years now! However, recently their support has started to suck. Yesterday, I had a support ticket for a very minor issue; almost 24 hours later, the ticket has not been answered. Very disappointing, and I can see why other forums in this space have switched away from vbullein. I'm certainly looking at, and open to, all other options.
I think it's worth doing for future point of view. As it's the best forum software for now.
For vBulletin upgrade it costs $209. Annual Phone and Ticket Support $199.00/Year.
For Xenforo it costs $140 for new.
Includes 12 months of ticket support and upgrades. Support and upgrade access can currently be extended for $40 for an additional 12 months.
XenForo has the ability to import data from other forum software, a process also known as converting. Version 1.2 of XenForo supports importing data from vBulletin 4.x. https://xenforo.com/help/importing/
When you get a PM from someone, you can see it.
Alert feature is awesome for more user engagement. When someone tag you or quote your post like I have done above you get alert for it.
Same goes for watched threads, whenever someone posts on your watched thread you get alert for it.
Social Engagement :-
Keep your users coming back by letting them earn trophies for reaching milestones. An intuitive "like" system makes users feel appreciated for their contributions, while integration with Facebook allows easy registration and sharing.
Recent Activity Stream :-
Allow people to easily see all the recent happenings on your forum, beyond just the messages posted. Members can follow each other to get their own personalized news feed showing the content they want to see.
Make it easy for users to stay up to date with updates that are applicable to them. They'll receive alerts when someone quotes their post or responds to a status update, when they receive a new trophy, and more.
Great Add-ons :-
XenForo is built to be the most extensible and flexible community software ever. Check out the huge array of add-ons already available in the resource manager, or get help writing your own add-ons with the XenForo framework.
SEO Built-in :-
With XenForo there is no need to pay more for your search engine optimization needs. Human-readable URLs, semantic HTML with embedded microdata, and many more SEO features are present in the very core of the system.
Don't take my words for final decision, check yourself.
Many people are ditching vBulletin and going for Xenforo. Some are going for other top forum softwares.
But I feel Xenforo is the best one among them.
Also if you move to xenforo, then I would recommend you to sell your vBulletin license if possible.
That will recover your money investment on Xenforo.