I have used vbulletin for a number of years, latest version for me was 4.2.
I recently made the change to xenforo as I was fed up off the lack of support from vbulletin and the constant number of security hacks, including google redirect problems.
First impression was that it was much cleaner, more upto date and had a lot of the features as standard I required unlike vbulletin.
I am now running the forums and can report the following -
1 - website much more upto date
2 - no security problems
3 - no redirect problems
4 - excellent support from the xenforo team
5 - fantastic selection of add ons, paid and free
6 - site seems faster
7 - very easy interface to import my original vb4 database over
8 - easy navigation around the admin area
9 - better integration with facebook and twitter as well as others
10 - I've never looked back
So, thank you xenforo.
One happy customer