Metriclima aurora is a mild one. The problem is that only the dominant male colors up. Occasionally a second male will color up and sometimes will lock jaws, etc. But I've never had them kill each other.
In general, I think the Labeotropheus and Labidichromous are pretty mellow for Mbuna and good citizens in a community tank. Note, I have not kept them all, but in my experience, they are good.
Also, Melanochromis exaspertus is a pretty docile fish.
Agreed to stay away from Kenyi.
I'd also avoid pseudotropheus desmani.. I had one that killed about a dozen tankmates before I figured out who was doing it. They are small, but very aggressive.