-African Cichlids from Lake Malawi grow to around 4 or 5 inches usually (the common ones, like yellow labs/electrics or red zebras), but are very aggressive towards other fish, even if they arent going to consume them in any way.
-Africans from Lake Tanganyikan grow about the same size or larger than the Malawian Cichlids but vary greatly in their degree of aggression. Some common Tanganyikans are herbivores, some are carnivores, and some are omnivores. They are a little more expensive and hard to find than the Malawis but in my opinion are more varied and look more beautiful.
-American Cichlids are usually grow about 6 to 12 inches. They are aggressive towards anything that isn't an American Cichlid and will eat any small fish. They arent usually as aggressive as Lake Malawian Cichlids (unless youre talking about a Red Devil). In my opinion American Cichlids move a little slower and fluid than the fast moving Africans.
-American Dwarf Cichlids usually grow around 3.5 inches long. Dwarf Cichlids (like larger American Cichlids) usually need alot of care but may be put in community tanks due to their peaceful disposition. They may seem bullies but wont usually actually attack other fish.
-American (larger and Dwarf) Cichlids need quite a bit of care compared to Africans but Dwarf Americans can be put in community tanks. African Malawians tend to be very aggressive to anything other than other Malawians (but they can be put in a tank with an American Red Devil). Tanganyikans have a high level of care (compared to Malawians) and are more expensive and rare but have some amazing physical and behavioral traits. Whatever you go with, you should be careful to place Cichlids with like sized Cichlids from the same area (usually) with the same levels of aggression.
-Personally I would go for a 40 gallon Tanganyikan tank of a Duboisi, a Moorii (Kaiser II) or two, a Cylindricus, and one or two Orange Leleupi.