>>2769312While it is true that people prefer Pepsi in a Central Location Test or "sip test", this is due to its sweetness and lemony burst. It turns out that when you ask people to actually drink an entire can of it, about half the people prefer Coke and the others prefer Pepsi. Pepsi's sweetness can get cloying when you have to drink a whole can and the citrus-burst seems to fade, whereas Coke has a raisiny-vanilla flavor that's quite consistent. Since it isn't as sweet, people don't like it when they have a little sip.
Malcolm Gladwell wrote an extensive article about this lol.