Natespf is correct about the Pepsi Challenge. It has been debunked by numerous marketing studies.
The Pepsi Challenge only works with small servings. In small 3-4oz servings, the sweeter beverage, namely Pepsi, wins. However, when blind taste test participants are asked to finish 12oz servings and compare flavors CocaCola Classic wins by a hefty margin.
But, when you start switching labels very bizarre things happen. When sampling Coke from a bottle marked Pepsi, the results are all over the map due to preconditioning and brand recognition.