There is no "best" dog food. If you ask 100 people what the "best" food is, you will get 100 answers, none of them wrong.

The brand that one dog loves, another dog will hate. The brand that one dog thrives on will make another dog ill.

I own a boarding kennel, and I see dog fed everything under the sun. I board a seventeen year old lab/pit mix that has eaten nothing but Ol' Roy (very cheap food) his whole life. He is very healthy and happy, and going strong at a very old age. I also boarded a schnauzer that ate nothing but the best brands of food, and died at six years of age from kidney failure. Food is not necesarily the end all be all of a healthy dog.

I personally look for a food with meat as the first ingredients, as opposed to grains. I don't feed the cheapest stuff, but neither do I always spend a small fortune on each bag of food.