I don't think there is such a thing as a best food. The key to health is a balanced diet. This should include live, frozen, freeze-dried, and pellets. I can't get my knife to accept cichlid pellets as yet, but I'll try again after the move.
I feed live ghost shrimp, black worms, and cut up earth worms (red wigglers) whenever I go to the "good" lfs. He gets a lot of frozen mosquito larvae and blood worms. As a general staple he gets FD blood worms and tubifex and prepared shrimp pellets.
I have never fed beef heart, but some people swear by it. The problem that I have is that it is not similar to anything in their natural diet and it is high in cholesterol, but I don't know the stats on most of the foods.
Brandon