Amiable: Some large cichlids, such as the Severum, are quite amiable and can be kept in a community environment. Angelfish are also quite peaceful. Discus are comparatively peaceful, but because they are also rather delicate and need care taken in their environment, are generally only kept in groups with other discus.
Relatively mild: Large cichlids like the Firemouth Cichlid, are relatively mild and they can be housed together.
Moderately aggressive include species with the nature of the popular Jack Dempsey and the Salvini Cichlid.
Very aggressive include species like the Red Devil and the Texas Cichlid. These are best house singly. or as pair in a very large tank, having lots of rockwork with escape routes away from the aggressor.