Article: As noted above, all of the tiny differences between Coke and Pepsi are easier (though not exactly easy) to notice when you can compare both drinks (rather than tasting one and trying to guess what it is). To stand a better chance of telling Coke and Pepsi apart, have both drinks available and ready to drink so you can try one and then immediately try the other. If you're doing this for entertainment purposes, have a friend blindfold you and scramble the drink containers so you're not sure which is which. If you're training to be able to tell the drinks apart in the future, feel free to leave the blindfold off. Your first action should be to take only a small sip of each soda. While everyone's sense of taste will differ, this test isn't quite as random as you may think. See below: Statistically, more people tend to prefer the taste of Pepsi after just one sip. Its sharper, sweeter taste makes it create a stronger impression. It can even caused increased stimulation in the part of the brain responsible for judging flavors. Now, continue to drink both sodas until you run out or you start to feel full. Take note of which soda you were more comfortable drinking a large amount of. If your preference switched (that is, you preferred one soda for the sip test but the other once you drank more of each), you're like most people. See below:  Statistically, more people tend to prefer Coke when drinking an entire can or more. Its smoother, less sweet flavor makes it easier to drink large quantities of it.  Thus, if you liked one soda better after just a sip but liked the other one better once you drank more, the first one was probably Pepsi and the second was probably Coke.

What is a summary?
Have both sodas for comparison purposes. See which you prefer after a sip test. See which you prefer after drinking as much as you want.