Is it better to give your cat a variety of brands and flavors of food or the same food all the time?

I know my question is a little confusing, but I was wondering will my cat like it if I feed him the same brand of food all the time or different brands? Also, should I feed him the same flavor, or is better to switch it up? Oh, and a lot of people say that "wet" cat food is not good for them and you should only give them that kind of food once in a while. How is it bad? I feed my cat about 3 packets or cans of wet food and nothing has ever happened to him.