Pepsi has a sharper taste, and coke is a bit tamer.
If you like super ice cold beverages, that possibly get water down by the ice, pepsi is more likely to be your drink, since it has taste to spare. if you like something with a bit more subtlety, then coke is more likely to be your drink.
There's nothing wrong with either preference, but I find them to be different enough that I can see why someone might logically prefer one over the other.
Personally, my drink is original recipe Dr Pepper, which you can easily get here in texas. It's even smoother than coke, the sharpness is almost completely gone.