Whatever you choose, you have to make sure the fish are from the same region. By that i mean if you go with South American fish (green terrors, oscars, ect.), then they all have to be south american (with few exections like plecos and catfish) and if you go African, the you have to stick with either fish from Lake Malwai or Lake Tanganika(spelling) and as far as i know, you can mix tanganika and lake victoria fish, but they're harder to care for and not as colorful. Then theres the Texas Cichlid from well, Texas. and it required different conditions as well. Its really about the Ph levels of the water b/c it varies greatly. Also different cichlids like different decor. Personally, I would prefer to have Lake Malawi Cichlids. They are colorful and common. They like a rocky terrain with pleny of hiding places. Also before you choose, check out their levels of aggression and choose accordingly. a mellow cichlid with an aggressive one is sure trouble.