The thing with mbuna is that they rather live in large groups of their own species. It is also safest to have only around 4 or 5 different species in a tank becuase they are very aggresive, breed like flies and with the wrong mix, very easily produce hybrid offspring which is not good.
If you go with an all male hap tank you options are almost endless especially considering your tank size. You will never have to worry about breeding and the assortment of colour is amazing. Lone males live together well which can't be said for an all male mbuna tank. Even the most experienced fish keeper has trouble with all male mbuna.