Humans, obviously.
At least that’s the answer I received when I asked my cat, Sam.
He went on to explain that while it’s true that, in many cases, humans choose and care for their animals, often it is the animal that selects the human as pet.
I am Sam’s human-servant and, when he’s in a favourable mood, his ‘cat daddy’. When Sam isn’t in a good mood, or when I fail his expectation of me somehow (as I often seem to do), I am his pin-cushion, kibble-boy, and often prey-to-be-hunted.

Sam says that cats, parrots, most lizards, hamsters, and spiders choose their humans as their keepers. All other members of the animal kingdom just end up as pets. (According to Sam, dogs are particularly subservient, and so loyal and dutiful to their humans that he insists they’re closer to plants than to animals.)
I do my best to be a good pet for Sam. He tells me that the worst pets are people who are in denial about their role as ‘human-servant’. Of course, the lower animals that submit to their human keepers are simply pets themselves. But, before he chose me when he was living in the shelter, Sam met a few cats that had what he called ‘dependency issues’. These cats choose pretty shitty humans who, in Sam’s view, should be made into kibble rather than occupy a home with another animal. They’re cruel, neglectful, and in rare cases completely felicidal. These humans are the absolute worst pets, but cats keep adopting them.
Sam is happy with my service. Most days, Sam will grace me with praise. When I bow to him, stooping very low to show respect to his exalted status, he will lunge upward on his hind legs to snuzzle me on the chin with his forehead and nose. If I am sitting, he will jump onto my lap, knead my belly, then crawl onto my chest and lean into my face. Suffocating me with his fur, Sam reminds me that his favour is more valuable than the air I breathe.
Overall, I’m a very good pet; but I know there is much I can improve upon.