It is very hard to gauge aggression from species to species when in a fish tank. Fish will often become more aggressive in smaller tanks due to the natural size of their territories in the wild. Are you looking for bragging rights or simply a glass banger? Bragging rights will be hard to fulfill. As for a glass banger, anything in the amphilophus, nandopsis or parachromis families will suffice.
Your joking right?I wouldn't go as far as to say anything in those families. Maybe for parachromis?