Oh that? Well, I can tell the difference right out- Pepsi has this distinct stretch of a flavor, while Coke just tastes acidic. It probably has something to do with the fact that you literally cannot get Pepsi at the fountain in the US Southeast, though, which does nothing to help Coke's case, besides the fact that I prefer their mortal enemy. Give me Pepsi's fizz anytime.
I've been drinking Pepsi Throwback recently, actually. Sugar instead of corn syrup makes soda taste a bit more- valid.