This is what happens when the two substances mix:
The experiment baking soda and vinegar is deceptively simple: what appears to be one reaction is actually two, happening in quick succession. This reaction is an example of a multi-step reaction.
What actually happens is this: the acetic acid (that's what makes vinegar sour) reacts with sodium bicarbonate (a compound that's in baking soda) to form carbonic acid. It's really a double replacement reaction. Carbonic acid is unstable, and it immediately falls apart into carbon dioxide and water (it's a decomposition reaction). The bubbles you see from the reaction come from the carbon dioxide escaping the solution that is left. Carbon dioxide is heavier than air, so, it flows almost like water when it overflows the container. It is a gas that you exhale (though in small amounts), because it is a product of the reactions that keep your body going.
What's left is a dilute solution of sodium acetate in water.
Basing my opinion on these facts I think that the "put the baking soda down first," will work best.