Someone with too much time came up with a county-by-county map of dialect differences for referring to soda (though I still think 'coke' fails to refer to anything that isn't at least cola, regardless of how many people use it with that intent). A breakdown of percentage of people shows what the other map doesn't, that 'soda' is the majority term.
It quite amazes me how many people don't know that 'pop' refers to what's basically a piece of candy on a stick that you put in your mouth and suck on. But then many of these are the same people who don't know what a bubbler is, instead referring to it by the word for statues in parks that spit water out of their mouths. 'Drinking fountain', however, is acceptable but too long for casual use. It would be like using 'carbonated beverage' for soda.