Which dog food is better, Purina or Iams?

I have an 8 month old German Shepherd. I am currently giving him Iams, for large breeds. I give him this food only as a base, I make my own dog food. Even as a base, I want to know which is better, Purina "Beneful Healthy Growth for Puppies" or Iams "ProActive Health Smart Puppy Large Breed"?