They are different fish, If they were identical they would have the same name. They are very similer because they are from the some genus. But there are differences. As far as intelligence goes I don't think one has a advantage over the other. I can tell you speeking in general that the midas males do tend to get bigger and more aggressive them devils. But in captivity the rules can change. I aquired 4 wild caught labiatum. I was trying to breed them but all 3 turn out to be males. One out of the batch grew like crazy. The other 3 all had the typical labiatum (devil) look, but the larger one look to be a midas (citrinellus). I did alot of research on this and got the same answer from 3 of the people I had contacted. In a nut shell this is what they said.
"The specific exterinal traits of these two species are subject to great variabilty in capitivy. They therefor often overlap so that detenmination is impossible by a visual inspection in the aquarium. It was also observed that the larger lobed lips of the labiatus decrease after time of keeping in captivity. It is obvious that certain external stimuli that induce growth in the wild is absent in the aquarium. only freshly caught wild specimens will display this trait. The protruding hump is not a genetically fixed trait to the citrinellus species. Capitive labiatus can also exhibit this feature as can many other cichlid species."
Bascially in a aquarium it can be impossible to tell the difference between a pure devil and pure midas. with out disection and inspection.
) I have heard they are about the same in aggresion levels but midas' are more intelligent? Thanks for your opinions. 
