I have really enjoyed the results from using New Life Spectrum foods. I have been using this brand for almost 2 years now, and personally, I believe my fish looks great! Check out the link in my signature area and see for yourself!
I will also add that regardless of the claim that they should eat only this food, I still have an extremely varied diet for my cichlid and my community fish. For instance, my Blackbelt is fed Jumbo Min Food Sticks, NL Spectrum -(large or Jumbo fish formula), OSI "Soft and Moist"-large pellet (spirulina), and OSI Spirulina Wafers. I vary these on a regular basis, but I also add fresh vegetables such as: Cucumber, Squash, Spinach, Zuchini, and even an apple slice once! I also occasionally give him Frozen Krill and some feeder ghost shrimp as well!
I personally believe that variety is the spice of life, and almost guarantees getting the right nutrients to your fish.