We use Gerrit at work, and having tried numerous tools in the past, we've settled on Gerrit because it's efficient with our time and is focused on doing CRs well. Things that I enjoy:

* Keyboard shortcuts. * Inline or side-by-side comparisons * Patchsets from changes * Makes it easy to check the change locally * Easy inbox/dashboard for CRs * Provides structure to passing code reviews (not everyone should be able to +2 a CR) * It actually has an interface that is useful