I've created a clone of my vB3.8.4 forum so I can try out a conversion of both XenForo and IPB3.2. I didn't want to buy both packages but I could not decide which one was best for me, without giving them both a thorough test, to see how well they converted my forum, and also test the all important tech support.
XenForo was, frankly, bloody amazing. My 160,000 post forum imported and rebuilt itself in almost no time. Posts were all there, users were present and correct, attachments all imported. Soft deleted messages remained soft deleted. I could have gone live with the converted forum within a couple of hours. This is the first conversion which I can describe as "painless". I can't comment on how good the tech support is because I haven't needed it yet.
Didn't have such luck with IPB3.2 I'm afraid. All attachments were missing despite having been imported (subject to an ongoing tech support ticket and a "patch" required), imported smilies didn't parse, custom BBcode went wrong, soft deleted messages were all converted to a "queued" status, members randomly given X number of likes and other oddities that will require some time to iron out.
I'm at that age now where forum software and conversions is a PITA rather than a source of excitement, but using XenForo for the first time from the admin side and I find myself having genuine respect for a quality product that actually works and getting momentarily excited before I regained control and reverted back to being grumpy.