coloration has nothing to do with my choice; I think africans have greater diversity, diversity which overlaps American cichlids, at least that which is regularly available in the hobby.
Tiliapia are direct equivalents of large CA bruisers. Mbuna are great either in a tank of their own, or as excellent dithers for larger fish--there is NOTHING out there that has the varied fishkeeping uses of mbuna. Malawi haps are excellent, active, beautiful streamlined predators, it is very fun to watch them wipe out schools of small fish, and their beauty is impeccable. Tanganyikans are mre placid, sedate,predators, and they have much different morphology. Jewel cichlids--, all the various species-- are of a separate morphology and behavior type as well.
The american herbivorous species hold no appeal to me; i like predators, or at least aggressive little multi-purpose thugs (mbuna). The only thing American cichlids have to offer me are the tilapia-equivalents, pike cichlids, and the mighty peacock basses.
This isn't to say i don't like American cichlids, but if I had to choose a favorite, I would DEFINTELY go with africans.