My animals all seem to require different things and, as such, get different diets. Feeding time in this house is fun.
One cat has a problem with bladder crystals, so is fed 1/5 can Hill's c/d in the morning and 1/4 cup of dry in the evening.
The other cat gets the same. She hasn't had any issues, but it's good maintenance and her coat is shiny. Doesn't hurt.
The mini American Eskimo we have has teeth problems -- she has an underbite, and she's cursed with the horrible "small dog" dirty teeth, so has been put on hill's t/d prescription diet (yes. It's an expensive food bill we carry). She also gets a teaspoon of canned go! every night as an extra. The go! is better food than I myself eat on a day to day basis!
We also have an 80 lb boxer/rotti who very full of energy -- we considered the raw diet, but it doesn't fit into our lifestyle very well, with the thawing, etc. And camping would also make this difficult. She is also allergic to corn and corn products, so dealing with her runny stools is definitely not an option. We opted to put her on Orijen -- it's the closest I've ever seen kibble come to the raw diet. She seems to absolutely love it, and fills up pretty good. Not completely, but I'm of the opinion that she will never feel completely satisfied! She also gets a portion of the canned go! at night.
All four of them get pieces of chicken/beef/bison/moose whenever I cook dinner.
I work at a vet clinic, and they actually recommend Purina's vet diet for most maintenance diets. There ARE corn by products in the food, but they apparently have specific proteins that are necessary for clean eyes, coat, etc. I've done a few in-services, but I'll admit that not a lot of the information stayed -- this happens when I get interrupted by customers and phone calls! The stuff is guaranteed, though -- if a dog doesn't like it, or the owners don't like the smell, or an animal is allergic to it -- Purina offers a 100% money back guarantee. This in itself speaks volumes -- I don't know of any other pet food company that will back this kind of guarantee up without a fight.