We think that the soda that fizzes the longest is A and W root beer. My science group tested the question and figured out that the amount of sugar in the soda counts. So even though we didn't test all the sodas, I'd say that the soda with the most sugar will fizz the longest.
Scientists have not yet been able to determine the answer to this troubling question but there is some hope that the Large Hadron Collider will provide a solution. In the proposed experiment each type of soda will be accelerated to 93% c (the speed of light) and then forced to collide with a stream of protons.The resulting spike in proton density will create a small black hole that theoretically should suck up all the fizz in the vicinity without annihilating Geneva. Any soda that doesn't lose its fizz under these extreme circumstances will clearly be a winner.