Are we talking about African or American cichlids?
If American, I'll have to say...Sajica. Maculipinnis aka ellioti is pretty bright too. It it really has to be under 5". I'll have to go with Sajica, Convict, or Spinosissimus. My dwarf cichlid (L. Dorsigerus) is one bright fish as well. Really, it is hard to say...
I would have to say J. transcriptus, although my A. calvus's are pretty smart too.
Dwarf cichlids (west africans and americans) that I have owned don't come off as too intelligent to me. But it's nice, because they don't make a corilation between me and food .
First you've got to define intelligence.
Do you mean trainability? Problem solving? Responsive to people? The ones that make you feel as if they like you when in reality they are just working you for food?
Awfully hard to determine the intelligence of a species when you don't know their thought processes.