Feed what is best for your dogs-what they respond to.
I don't like Purina or any of the common store brands because I have seen the difference from a dog eating Purina and then switching to a 'higher' brand of food(Natural Balance).
I feed my own dog Natural Balance- Because their food is grain free and it's what my dog responds best to. My own dog has sensitivity to grain so any of Natural Balance formulas are what my dog responds best to-so that's what I go with.
As mentioned before I have seen the results of a dog switching from a lower food(Purina) to a higher quality food(Natural Balance).
This is that situation:
My father owns a dog-a mixed breed- who is now ten years old. Her whole life she was fed Purina, she didn't have any major health issues. She would get constant ear infections, but that's it. Physically, she always looked skinny. Her ribs and hips would show, as would her spine. She has always been free fed and also fed scraps but she just wouldn't gain weight. Her energy level has always been so-so.
Two years ago she was switched to Natural Balance. Within a week one could easily see the difference-physically. Her coat became softer, her energy went up. Her ear infections started lessened and within a week-she filled out. Not so she was fat, but she looked healthy-fit. When my father took her into the veterinarian-he was amazed at the physical changes and also other changes. Her gums were a lot healthier as were her teeth.
Similar changed happened with the family cat, she too was fed purina her whole life. Last year-when she was nearing 17 years of age- she started to lose her fur, throwing up, had less energy, etc. The veterinarian couldn't find anything wrong with her. After seeing the change in my father's dog, my parents thought 'why not' and switched her food to Natural Balance too. Again right away, one could see the changes. Her energy came back, her fur stopped falling out and became very soft. She also stopped throwing up.
It's amazing what simply changing an animals food can do for them.
You can also try feeding your dog a raw diet.