My betta fish hate pellets and flakes and since that's not what they would be eating in the wild, I like to feed mine a strictly frozen and live-based diet. Mine get a rotation of bloodworms, brine shrimp, daphnia and various mosquito larvae and other insects I find like gnats and flying ants etc.
I have yet to have a problem with feeding this diet, and it's amazing what the added protein in the frozen foods can do for ripped and damaged fins. One of my males tore his dorsal fin in half, and it had almost entirely healed by the next day.
I used to feed flakes and pellets, but the ingredients left a lot to be desired and so I decided frozen was the way to go. Now I just have to stop everyone from jumping out the tops of their tanks when they see me coming with their food container