I have a dog on the CD Science Diet.
Why does your vet want you to change? Could you ask him what the real difference might be? I don't know anything about the RC Urinary diet.
I can only say that my dog has been on the Science diet for a few months now, doing well.
Your Vet wants to change his food because He (Your Vet) makes money off of selling YOU, Science Diet! I bet he doesn't sell Royal Canine, does he? There's your answer.....Price wise, they cost about the same...RC may be a little less. I think the RC is better....My dog liked it better, also....Stick with your original thinking and just tell your Vet that your happy with what you have.....Just say you've tried it before and your dog liked the Royal Canine, better. :) Hope this helps...Karla