I have learned that vets are not nutrition experts when it comes to pet food. Matter of fact, many feel obligated to push specific food brands because of the kickback into veterinary schools... Science Diet being the biggest. And it's one of the worst foods on the market.
Just to say that even though your vet may be a great doctor, he's not a nutritionist, and they do have ties to companies that support their schooling and practice. So don't always take their advice as the end-all.
Your food should have NO fillers in the top 3 ingredients - esp not corn. Dogs need meat, not crap. Good foods will have 3 major sources of protein in the top 5 ingredients or so (NOT byproduct, real food)
Harley is now on Nutro Natural Choice Ultra, a new top of the line natural premium food by Nutro. He loves it, but he'll eat anything. Thank goodness he's not picky. It's affordable, he doesnt' have to eat as much, it's good for him, and his output isn't as much so it lasts longer. DH and I just went to PetsMart and read labels, based on info we got from various online sources and dog experts. I have heard AWESOME things about Chicken Soup foods too.
There is lots of info online as far as good foods and how to tell. Good luck in your search!