What is the best food for our Boxers health?

With so many dog foods out there I wanted to ask Boxer people what they believe is the healthiest food to give them. I have a three year old Boxer and a four year old Boxer who is gaining weight. At first I just thought it was due to winter and like the rest of us we tend to gain weight during the winter. He is usually pretty active and especially now that we’ve just adopted our three year old. We feed them iams but wonder if there is something better. I admit that we do boil chicken breast and mix a little in their food, is that bad?