I fit for where I grew up it's POP, and honestly everyone I know here in southern Oklahoma calls it pop too, i'd bet the statistics are skewed here due to all the soldiers in and out around this area.
Being from California... it's soda. It drove me insane when I lived in Texas and people called everything "coke". The amusing thing is that I learned how to talk in Chicago; so I grew up calling it "pop". But then I got made fun of after we moved back to California when I was 6.... so I started calling it soda instead.
In 1772, English chemist Joseph Priestly succeeded in duplicating nature's bubbling mineral waters by passing carbon-dioxide through ordinary water. At that time, as even now, sodium bicarbonate was used in medicines and for making baking powder.Known as soda bicarb, it was produced by bubbling carbon-dioxide through a solution of sodium carbonate obtained from the ashes of plants.