Most foods have basic nutrition information (protein, fat, etc) printed on the package, though I doubt that 48% protein is really different than 46% protein...
A combination is likely best for marine life, just as it is for people, though each fishkeeper will have her own personal preferences. I think that flake is a good staple for fish and for those corals that will consume it, because it has vitamins added.
You might actually get more and better responses to this question in the general reef discussion forum, like the above announcement suggests, since this is not an advanced topic.