Don't get me wrong... I am longing for a replacement of vBulletin, especially after the entire v4 debacle (which I refuse to pay for). I am a "old-school" vBulletin webmaster with 3 very large and established vBulletin communities.
And while I am excited to find xenForo, what's the sales pitch?
What will make xenForo a better option than vBulletin?
Thanks in advance for your time.
If you do a side-by-side comparison of features, then vBulletin will win.
However, if you ask the question "How easy is it to style and customize vBulletin?" and "How easy is it to write Plugins, CMS, Blog, etc. for vBulletin?" the answer to both is "extremely difficult".
XenForo is designed from the ground up as an MVC application. This means that instead of Plugin authors being limited by which parts of the code have the right 'hooks' or being exposed in the correct way, XenForo is fully extendible. At every point in the code, it is possible for a Plugin to change or replace functionality of XenForo without breaking the rest of the forum. In vBulletin, a lot of functionality people wanted could not be written as a Plugin because it required too much 'core' functionality to be changed.
In XenForo, I can change core functionality with a Plugin, so as a result, all of those features which have been bolted onto the vBulletin core over the last 8 years can be done as Plugins. Also, XenForo has built-in support for content types. The forum is just one content type, and Pages are already another type. This will allow people to add all sorts of content directly into XenForo without it feeling like an ugly hack or bolted-on feature.
And the Style system is just a revelation compared to vBulletin 4 which is almost impossible to style. Most of the professional style companies that built and sold styles for vBulletin 3.x have withdrawn from the vBulletin 4.x market because of the difficulty and poor customization support.
bottom line:
If you are just looking at features, and want to run a 'stock' forum, then vBulletin may be a better choice for you. But if you want a forum that encourages customization, and will quickly have a huge community of Add-on development, then XenForo is the place to be.