I'll go with domestic cats. Aside from the problem with the litter box and keeping them from scratching the furniture, they are not as problematic as dogs, for instance.
Oh yes, I do have another favorite animal - the Warthog. A creature that engulfs all of natures indomitable talent for beauty and represents a spitting image of that Boadicea of the North, the Icon of the Arctic, our very own real life Eskimo Nell - Sarah Palin - who scared the living daylights out of the Democrats during the last US Presidential elections.
Good question I have numerous animals here on the homestead, dogs, cat, rabbits, chickens, turkeys, goats, horses,pigs, lets see what else oh ya bees.