there is no one best food. a good varied diet, including different frozen or live shrimps, worms, with a good staple pellet, as with any fish. you can use any of the better commercial foods like hikari and have great results. or even spend some $$ and buy specialty FH foods if it made you happy
when your FH starts getting quite large and beefy, try ordering from kensfish.com. he has a 7.5mm cichlid pellet that is bigger than any of the commercial foods available. perfect for large fish. my FH seems to be doing well on this exclusively, since he's a picky eater.