If you stick to just one flavor, eventually your cat will eat nothing but that flavor. Using different flavors of one brand, or different brands of the same quality, would be preferable. If he has a sensitive digestive tract, you could mix the new food with the old, gradually reducing the amount of old food given. Our cat has an ironclad stomach, and gets three different brands of dry food and four different brands of canned food (in about 10 different flavors) a week! Some cats just insist on variety. Go slowly, and see if he has any trouble with diarrhea. If not, you can offer him some assortment. If you are now giving him a high-quality brand like Nutro, you could try something like Felidae, Solid Gold, Innova, Precise or 1st Choice. I'm sure that others here can recommend other foods available in your area.