Q. What is the best dry dog food for a Border Collie?
A. If you're truly looking for the *best* food for your dog, look into feeding a well balanced raw diet. I feed my dog Ziwipeak, which is an air-dried raw food-type diet. It is well balanced (so I don't have to worry about attempting to balance a diet myself if I were to be feeding raw food).
Ziwipeak is very expensive though. If you're looking for a kibble specifically, look into Taste of the Wild, Orijen, and Merrick - these are high quality kibbles.