Realisticly (as if we care), I'm pretty sure 'pop' and 'soda' is a difference of regional dialect. In fact, I'm under the impression that in some places, if you just say pop they assume you mean coke specificly. I say soda, mostly because that's what everyone I know calls it. Of course, if I was visiting someone like an illustrious doctor of languages I would call it whatever the heck he told me to.