We're transitioning to Xenforo. They've been the leader the past few years, started by the guys who left VBulletin when the company was bought out. It's mobile friendly, super fast, an easy transition for VBulletin users, huge amount of aftermarket addons, etc. Cross-browser friendly, etc.
I hope to have a beta preview available by the end of this coming week.
User passwords and ids will remain unchanged. There are a handful of users I'll need to email to let them know their user id has changed slightly (Xenforo does not support commas in user names). Our case is a bit different from most VB to XF migrations, as I'm having to write custom PHP code to replace some of the custom code already in place to support TDR magazine subscriber integration.