Almost any cichlid, excluding oscars (lol) can be incredibly aggressive. You see, if someone has, say a green pike cichlid, in a 90 gal for a year alone, then any fish you add will be in danger.. same with any other fish. Adding a new fish to an aquarium is always a challenge, because as soon as it hits the water it is stressed. There are always exceptions, but in the end, if you grabbed a full grown pike cichlid, red devil, jaguar, umbee, and dovii, and put them all in an aquarium they've never been in, chances are the biggest one would become dominant.. that or whichever one is naturally most aggressive. The thing is, I've seen doviis that hide, and ones that attack glass.. along with jags and other fish.. heck, a convict will do it if you make it mad enough.. honestly its luck of the draw.. Everyone has had their own experience, and that is what they post.. Doviis in my opinion, are the most dangerous, only because they have teeth and do the most damage.. honestly in the end its all your opinion.. but like I said, grab and jag and let it claim an entire tank, and in the end it will be aggressive if you add another fish. Also, males are typically more aggressive than females (breeding aside)