We found VB to be clunky, slow, outdated. When we took over we were on VB 4, and VB Connect test upgrades proved to be an absolute nightmare. We made the decision therefore to go with Xenforo, with Enhanced Search. Our migration was completed a few short hours ago, relatively pain free, and in a little over 24 hours. It probably could have been quicker if I didn't have 'life' to do at the same time.
We're using the UI.X framework from Audentio, and haven't made many customisations - a bit of colour changing here and there, and some small config changes. We'll no doubt make some subtle changes over time. I am incredibly happy with Xen, and our members involved in pre-deployment testing were so impressed we brought our migration date forward to accommodate them.
Take a look - let me know your thoughts. Let it be known however that if you're looking to migrate a decent sized database and have any fears, please don't - it really couldn't have been easier!