Puppy! But mostly because babies scare me. I like the idea of a kid, but my preference would be to get one when they're already housebroken/potty trained, haha. So, that cancels babies out. Puppies are easier.
I really don't like babies. And I really don't like puppies, either. But at least puppies grow up to be dogs, which I like, while babies grow up to be children, which I don't like. Logic.
That's easy. Puppy. I'm too old to raise another human baby. I might even be too old to raise another puppy. But if I have to choose one or the other, it's a no brainer.