Baby. Hands down. Dogs are really very easy, train quickly, and you can confine them during their destructive period. After that they're quite clean.
Babies can be in diapers for 3 years or more, throw food, throw up, pee, and poop. The amount of laundry a baby generates is staggering. The work a baby requires is enormous and that alone means other household chores don't get done when they should. Then there are the toys, the accessories, and all kinds of things that go in the dishwasher from breast pumps to nose syringes. You even have to get the thing its own bedroom! Then you face years and years of writing on walls, throwing-up on things, bed wetting accidents, tracking mud through the house, blowing stuff up, and possibly even wrecking your car or burning down your house. Kids are not for people who like minimalism or even a remotely clean house and do not have full-time staff.