I've had every fish named on this list and a full grown buttikoferi is meaner than a red devil, so are festae , trimaculatum, dovii, and adult umbrifrium..now don't get me wrong i had a 15inch red devil who was extremley aggressive,. but at the same time i also had large buttikoferi and dovii not mention trimacs that were absolutly insane...but actually for size if i had to pick the meanest cichlid it would have to be the good old cichlsoma nigrofasciatum[Convicts] they have the best adaptability and i've seen them try to fight fish way way bigger than themselves. and i'm amazed folks said red devils are the meanest. I've kept cichlids for well over 20 years and has mixed many many species including species that are from the great rift lakes..