It’s not possible to give a simple answer to your question. The best food depends on a dog’s age and life stage, their activity level, and their state of health. A veterinarian who knows your dog and any health problems that he or she has is the best person to advise you.
An information source that specializes in dogs and is written by a vet could also be useful. It would be good to look at several sources. Even experts sometimes have different opinions. One helpful source might be the Merck Veterinary Manual, but there are others.
I look for a high-quality food that contains natural ingredients and doesn’t contain ingredients such as artificial colors, flavors, and preservatives. I look carefully at other ingredients in the food that may not be healthy, such as the salt level. I also do some research about the company that makes the food to see whether it has a good reputation and to see whether its claims about the food seem accurate.