I would also like to add, that looking for the "best food" is often easier to do when you look at it from a process of eliminating the worst foods and there's several things that you can look for to do this.
For me some of the things I look for as a bad ingredient are first and for most, corn, which have very little nutritional value, and in my understanding, is the absolute most commonly used filler in any "cheaply, or poorly made" food product. Another two I am not fond of are soy and yeast as these two are often used boost protein levels, and act as fillers, but this protein is not very digestable. Finally, any land animal, no matter what part it is used. The biggest 3 for me are corn, land animals, and soy. Just eliminating any food from the list of possibly "good food", and putting them into the "bad food" category will narrow out about 1/2-3/4 of marketed fish foods.
From there I look at the way the most desirable ingredients are labeled, trying to avoid the word "meal" after any of these ingredients, especially if it is one of the top 5 ingredients. By doing this, we don't necessarily need to remove them from the current list, but perhaps put them in a medium, or "ok" category.
Finally, delivery. While a dense pellet is naturally going to be more nutrient rich, due to the fact that obviously more ingredients were put into each pellet, and since we have eliminated 90+ percent of foods we have to look at this as a sign of lots of good ingredients crammed into each pellet. While flakes have I higher obsorption rate then pellets, I have seen dome company's trying to cut down on this. For example, omega 1 flakes have many small granules on each flake. These granules are denser then the "flaky" part of the flake, meaning more ingredients in each flake. Also, very light weight, and course pellets are going to retain more water faster then a dense one. Which means the stomach of the fish will be more full, with less nutrients, as tank water isn't nutritious. The same can be said for gel foods, if we have 50% protein, but are mixing 1 part highly nutritional food, to 4 parts water the nutritional value of the food must be cut in fourths, because of dilution. Best example I can give of this is if it is dinner time, and my children won't eat their peas, so I stick 2 peas into each spot in an ice tray, and pop out the desired amount of peas, lets say 20, my children's stomach will be full of water from eating 10 ice cubes, but they got the peas right? Well yes, but peas aren't the only thing on the menu, and how much more nutrients could we have fit in their stomachs, if we didn't have 10 cubes of water in there? What happens is the stomach is physically full, but its full of very little nutrition, and a lot of water.
I hope this makes sense, its my method for choosing the food I do. And, I'm pretty sure, that I have expressed all of this in an easy to understand, yet logical and informative way.