If I might, and if you're willing to spend the money, I would like to suggest
canned Wellness grain free. It's better for your kitties than the vet stuff, and because of its high calorie content, they'll eat less of it.
Also, I wanted to add, that even though Wellness is more than the Compliments brand, it's typically far cheaper than the vet Hills/Science Diet stuff, which is high in grains and not much else.