If your thinking in domestic terms, then i would say a dog because they need walking everyday, training a considerable amount to ensure that they don't develop behavioural problems and also to provide stimulation. In a way, they're like children and whereas cats can go off and fend for themselves, a dog can't do that and depends on us. Reptiles are pretty low maintenance when kept in captivity and most don't need feeding that often. Also, hamsters, rabbits etc are pretty easy to look after so yeah, i'd go for the dog.
My little brother? Lol I would have to say snakes... Cant stand em!!!
A Blue Whale