XenForo is the best forum software out there right now, IMO. It doesn't have the same everything+the kitchen sink feature list of VB or IPB -- yet -- since it's newer, but I think the lack of bloat is a plus and since it was built new from the ground up it has a much more modern and clean feel.
How is XenForo's admin panel? Easy to navigate, find things, good work flow?
I just find the IPB admin panel to be lacking. Lot of features, but then random settings that should be accessible via the admin panel require custom code edits. For example, the 'recent topics' listed on the sidebar, by default, shows 5 topics. You have to edit code to adjust the value to anything higher/lower. The hooks system was confusing at first, because the damned thing is shown in 3 different places but only one has adjustable settings. Blah.
IPB support is okay. Had a major issue a couple months back where I goofed on the 'archive settings', and somehow everything archived, meaning threads couln't be responded to. Was a huge hassle getting things 'unarchived', and even then not everything did. Had to do hundreds of threads manually. Then a large thread that had 900+ responses lost 13 pages of content... So they had to import that manually from an archived table back to whatever. But they did it, kind of.
Support is okay, I usually get responses in 30min - 1hr unless it's something strange as the archiving issue was.
I think it's too late to switch to anything else anyhow, but XenForo does look quite good.
I'd say there is an initial learning curve, like any full-featured software will have, but I was able to figure it all out without looking at any documentation.
One of the best things about XenForo is that it has what's possibly the best portal around for any forum software -- XenPorta -- available as a totally free mod. Check the demo link on that listing. Beats the pants off WordPress for most needs.