Natural choice isn't a bad food and it isn't like you chose to put him on Beneful or Pedigree garbage foods. If he is doing well, he is thriving, and you and your wallet are satisfied, I would say stick with it until you feel another change is in order.
I tried my boy on Orijen Large Breed Puppy, and although I bit the bullet and paid so much for the food (which I liked at the time and would currently promote), but after meeting another DT member in my area and having our dog's play (they are best buds!), I decided to switch from Orijen to FROMM which in my area is cheaper (and one of the only shops that carries it is within walking distance of my house), but the results I am seeing are phenominal results.
Poos formed and less waste produced and that icky dober-gas is minimal! Plus I feel his coat is softer and visually shinier!
It is all what works for you and your dog