While doing our other experiments we found that cans of regular Coke sink and cans of  Diet Coke float.  We conducted some research and found out that this may be because of how much each type of coke is filled up or it may be the formulation of the Coke/Diet Coke.

We ruled out that the coke may be filled up to different heights by measuring the 'mils' then confirming it on the side of the can.  We believe that it may be the formulation of the coke.

We found that the property which makes something float is called buoyancy. If a can of diet coke floats that means the weight of the can, plus air in the can, plus soda in the can, must weigh less than the weight of water displaced by the can. For a can of regular coke to sink, the weight of the can, plus the weight of air in the can, plus the weight of the soda must weight more than the water displaced by the can

We found that artificial sweeteners are more concentrated than sugar.  Because less weight of sweetener is very likely dissolved in diet coke, compared to sugar in regular coke, then the weight of diet coke is less than regular coke for the same volume.
Diet coke probably weights a bit less than regular coke per unit volume so it would be more likely that the can of diet coke would float.