I loved Phabricator. It’s the system that made the most sense to me, with no real issues. I was shocked when I saw that no more work was going to be done with it and I’m glad to see someone pick it up!
I never got GitHub's PR model. Maintaining separate branches of a single codebase is something I want to do approximately never, and a single commit is the right atom for code review.
Thus, I find Phabricator to be intuitive in a way that branch-based workflows never were.