Dog food question. Want help please?

My 6mo Lab/Pitt mix has been on Nutro max since He could eat. He's been fine on it. Only poops twice a day, and its firm and healthy. Should I change him? To BlueBuffalo or something great? I know Nutro is middle of the road. No byproducts though. Just chicken meal, grains, lamb meal, omega 3 and 6. Its not too bad. We give him a fish oil pill every night too.