Best dog food? Best cat food? Raw. Balanced.

Wild Genes
We know from genetic mapping now that domestic dogs share some 99% of their genes with the wolf, their nearest wild cousin, and ancestor. Similar overlap must exist with the domestic cat and the wild cousins and ancestors they have come from.

Tweaking Genetics

We, as the human species, have selected for very, very little other than appearance in our breeding of pets. (Much more selection takes place in dairy cows, for example, for the suspension of udders, production of milk, strong legs, etc.)
So, you find yourself attracted to certain breeds more than others, because they appeal to your heart, your mind, your intended “use” of that animal, etc.
You might be a person who rescues a certain breed. You feel good around that breed, and like being involved in rehoming those waifs that ended up homeless.
You might like the dogs that are big and trained to work, like in search and rescue, herding, seeing eye guiding, guarding, etc. There are breeds that just fit for you in your chosen avocation.
Small pets that can go with you and don’t cost much to feed or medicate might be your cup of tea.
Your goal in choosing animals might be entirely based on form over function. Or vice versa. Or temperament, like affection seeking, or protectiveness, etc.

The bottom line is, We have done nothing to select for a “new” digestive system in our domestic animals. Nada. Zip.