Moral dilemma: save the dog or the braindead child?

Let’s say you were put in a completely contrived position of being able to only save one life and you had to choose between a young child that was completely brain-dead and would be guaranteed to never have a single higher-level thought for the rest of it’s life, and a healthy dog. For sake of argument, assume that such a scenario exists where your only option is to save one of the two (it could involve trains, switches, evil villians, falling elevators, buttons or other contrivances to force you to make a choice).

Which do you choose to save and why?