Skip the Royal Canin, Science Diet, Iams. A Yorkie eats next to nothing, so the cost of food is minimal even with truly "expensive" foods. Plus, dogs eat much less of the higher quality foods. I spend less than $80 a month feeding 3 large breeds and a toy breed. Does your pitbull NEED the performance food? Diamond also makes Chicken Soup for the Dog Lover's Soul...it's a MUCH better food for both of your dogs-Higher quality ingredients, and only about $3 a bag (for the biggest-it's 30 or 35 pounds) more than the regular Diamond. Diamond Naturals would be a decent food that both could eat. To keep them from each other's food (if you feed different foods), simply feed them in separate rooms with a closed door between them. If I were to recommend an inexpensive food that both could eat, I'd go with the Chicken Soup (if they don't carry it already, anyplace that carried Diamond can get it for you). My dogs eat California Naturals, made by Natura, who also makes Healthwise and Innova. Those three, in my opinion, are the best foods out there. Some other good foods for both dogs: Wellness Super5mix, Merrick, some of the Solid Gold varieties, Prairie, Canidae All Life Stages. If you feel that the Pitbull needs the extra calories from the Diamond Performance, you could feed that the the small dog, as well. It's at the high end of what I would feed a small dog for protein (30%), but should work out fine, except that I would monitor weight closely. I searched high and low for a food that all 4 of my dogs could tolerate, because feeding separate foods is a huge pain to me.