My vet swore by Science Diet until he found out I wasn't worried about cost and that I was more concerned about the overall health and wellbeing of my dogs than whether I could get the feed for them at the vets office or the pet supply store. Once he found out I wasn't concerned with how much it was going to cost me to get them the best of the best, he recommended Eagle Pack Holistic. Eagle Pack is available to me in my town, just across town from a feed / specialty store and is way more expensive than Science Diet is.
My point is that I think you should make it clear to your vet what your intentions are with your pet. If cost is not a factor, then make that clear to them. Oftentimes, they get yelled at for costing too much or recommending something that does. Just because the vet said that the feed that your little one was already on was okay for him, doesn't mean he doesn't know what he's doing. It just means that there isn't a reason to change it unless you present him one.
