Smudge was on Royal Canin SO when he moved in, but it wasn't working, so the vet suggested Hill's c/d. Luckily, it works and he loves it. But it's really so dependent on each cat's body chemistry that we really were just lucky that he happens to enjoy the one that turned out to be right for him. (He also gets a little bit of non-prescription wet food, mostly as a bribe to get him to eat all the supplements & extra water I mix into it.)

Love, Columbine