My personal experience has been Mbuna. They work great with my Flowerhorn. Really quick, intelligent, a little too big to be eaten easily (flowerhorn could never catch them anyway) and they are tough enough to live with them. Just provide a hiding spot or two, depending on how many you have. And make sure they are the tougher Mbuna. I have Kenyiis with mine. Not only do that add tons of movement, they have the beautiful blue and yellow coloration. Just MHO.