We started off with GitLab so we're kind of used to it. It provides the following powerful anti-features: it's both more polished and far easier to use than Phabricator, which encourages lots of useful but esoteric and BOFH-style development processes like forced test plans, test coverage analysis, and pre-commit code reviews that take time for people to get used to.

Basically we're looking to leverage some more of these over time as we find the time to invest in the learning curve, without throwing away our lovely, easy to use, already functional, and far more polished GitLab system.