Pet value will tell you "their" brand (I can't remember the name) is the "best" and "the same as" most brand name foods. The fact is it is not!
Hills (Science Diet) and Eukanuba do the majority of research on new, better pet foods. Purnia does quite a bit as does Royal Canin. I like to support the companies that are putting the money and effort into finding better ways to feed our pets. Hills is #1 when it comes to "new breakthrough" feeding for diseases. They put a lot of the money they make from the sale of their "maintenance" pet foods into research for disease specific feeding as well as researching nutrition for every day feeding.
Purina makes some of the best foods available (there veterinary brad as well as prop plan), they also make some of the worst (chow). Hills only makes decent foods, Eukanuba is owned by Iams (which is owned by a conglomerate). Euk is great Iams used to be very good (seeing more issues with dogs on Iams than before they were bought out). Royal Canin makes some veterinary foods, and a lot of "niche" foods.
There is this thing lately that says "corn gluten is evil" it is not! It is 100% protein that is around 99% digestible! The "real meat first" means little also since grains can be broken down to many parts. Each of those parts then weigh less than the meat in the food. But, the over all amount of grain/filler can still be more!
Price means little, though you will often feed less of most more expensive foods. The companies out there not doing feeding trials and developing new foods, are simply buying the top 3-4 brands, breaking them down to study them then trying to copy that food. They may make a good copy, they may make a poor copy. Also, they usually add some "tag" to it to make it more sale-able to the humans buying ("human grade" "meat first" "all natural"......most top brands are also "all natural" they just don't feel the need to use that as a selling point, they use the fact their food is better to sell it)
Pet food is not as easy to figure out as commercials would lead you to believe. It is so complicated actually that often a rep cannot tell you the "difference" between theirs and a competitor. My former boss once asked our one rep to tell him why her "urinary diet" was better than the competitors based on ingredients and dietary values listed on the bag. She told him there was no real way to do that! How is somebody at a pet food store supposed to be able to do it? They are taught to sell their foods using "key words" that customers want to hear.
Bottom line. Basically a good food is one that your pet does well on. I feed either Science Diet/Hills, Pro Plan or Eukanuba. I Always, always, always raise pups on Eukanuba now. I can't take back their growth stage. If I cheap out on puppy food and it affects their growth I can't fix that and it may not be apparent until they are older. My adults that live with me eat Euk, Prop plan or Science Diet.