Frozen in my opinon.
Alot of flake food is baked losing much of the nutritional value to it. Frozen food is good if its fairly new frozen food. Avoid old frozen food or frozen food that has been thawed and refrozen making it freezer burnt. U can buy additives such as garlic gaurd from seachem that u soak ur frozen cube in before feeding to give if a more nutritional value. May i suggest buying flake or frozen that is inhanced w/ spiralina.