We feed our dogs Iams. Is it the best? I don't know, but here's why I feed Iams.
We had always fed Purina dog chow, our Shar Pei developed a rash (don't know if it's related to the food or not) anyway the rash was real bad, she was always scratching. One day I was at the store and saw Iams food with a Shar Pei on the bag, for healthy skin and coat it says. Literally one bowl of food, she never scratched again and the rash went away in a few days. It's been years and all good.
I'm sure there are better dog foods out there, just sharing my experience. I have 3 dogs on 3 different Iams formulas.