After researching the food and the ingredients, finding some accessible to your area, and within your price range, it is time to buy a bag and see how your dogs like it. If they like it they will eat it, and likely do ok on it. If they do not like it you are dead in the water.
If they like it and it does not give you the results you are looking for, proper weight, firm stools, nice coat, try the next one. Keep track of the ingredients of the foods your dog did not do well on, so you can compare.
I like Canidae. But even after major research, and finding the best food for your dog, it may not be the best food for YOUR dog. So let the feeding trials commence.
Oh, and dog foods change over the years too, the companies change hands, the manufacturers try to cut corners.