Believe it or not, there was a study of this, and they even produced a map of who says pop, soda or coke! Notice how this map is more detailed and apparently took more effort to make than ones that show who voted for Bush or Obama
In NZ, and Australia I think, small kids refer to them as "fizzy drinks". Older people mostly call them soft drinks, cokes or lemonade (which is Sprite or similar, not what you make from lemons)