I'm a dog person, but I'm kindly inclined to the Dog's historic rival in exploiting the human host. Not that Dogs and Cats are pure parasites, though the cat's role as a toxoplamsa vector arguably moves them closer to the dark side. Dogs do eat garbage and thus reduce disease (like toxoplasma, which can't live in dogs), cat's do kill pests, which reduces disease (do cats get plague?) and food loss.
Quibbles aside, as a happy host to my current canine parasite, I'll raise a toast to the strategic brilliance of the cat, an animal that went from chewing on primates to switching sides when the time was right ... (emphases mine)
The Near Eastern Origin of Cat Domestication (Science)
... Some 10,000 years ago, somewhere in the Near East, an audacious wildcat crept into one of the crude villages of early human settlers, the first to domesticate wheat and barley. There she felt safe from her many predators in the region, such as hyenas and larger cats.
The rodents that infested the settlers’ homes and granaries were sufficient prey. Seeing that she was earning her keep, the settlers tolerated her, and their children greeted her kittens with delight.
At least five females of the wildcat subspecies known as Felis silvestris lybica accomplished this delicate transition from forest to village. And from these five matriarchs all the world’s 600 million house cats are descended....
a subsequent NYT editorial comments:
Cats Among Us - New York Times
... This new genetic evidence resolves the puzzle of cat remains turning up in Cyprus before the rise of the Egyptian civilizations that were supposed to have domesticated the cat.
The wild subspecies that gave up their DNA for these tests still exist, though barely. That is one of the painful ironies of domestication. Creatures who come in from the wild eventually prosper — domestic cats number, after all, in the hundreds of millions — while those who don’t almost inevitably fall upon hard times...
Humans are the ultimate predator, compared to which the old saber tooths were ... pussy cats. We may not last long, but in the meantime we are pretty sure to wipe out every large animal that doesn't find a way to serve us. The cat made a good strategic move. With luck they might outlast us, and return to having primates for lunch long after we're gone ...