Mbuna such as Yellow Labs go with just about anything. They are less agressive than other Mbuna.
Peacocks are great, and there will always be posturing and aggression so the tank will never be dull. Other Haplochromes are often less colorful (excluding elecric blues) and very aggressive.
Tanganyikans are really great, and you can put a few varieties in a tank of that size, however, some can be quite aggressive when breeding. They are interesting and smart.
I think you'll get some very nice color and have an active tank if you choose Peacocks. They also get a little larger in body and finnage than Mbunas. They would be my first choice as a display tank. If you want to breed, then I'd go with Tanganyikans. Mbunas would be my last choice even though interesting, active and colorful. They are downright mean more often than not.