For a DIY experiment, I would be tempted to switch the feeds back and forth every few days over the course of a full season and observe and record the activity. You would have to establish a 1-10 scale, up front, knowing that you can maintain some consistency. I think this approach would allow the fish to become accustomed to both feed's differences and performing the tests over the course of a summer might allow environmental changes to be averaged out. In the end you would have a number rating for both feeds based on enthusiasm alone.
Not very scientific, but you could establish whether the fish like Prime Rib or Filet Mignon.
