A good way to compare foods in the store is to look at the first three ingredients... Personally, with the rottie/shepherd puppy I was fostering, I fed her Purina One for growing puppies because it has lamb as it's very first ingredient. This means more protein, calcium, and amino fatty acids. It also means less carbohydrates and THAT means less poop in the yard because the body can actually use more of the nutrients in the kibble!
Most 'cheaper' foods start with yellow corn or something like that... which is great for flavor if it's not one of the first few ingredients, but it's more of a 'filler', not a functional nutrient.
So, check the first three ingredients on a bag of food, the first one listed is what the main consistency of the kibble is made up of - this can help you decide what to feed your pup.