I grew up saying "pop" for the stuff that Coca-Cola, Pepsi, et al. make. Then I moved to the East Coast and quickly learned to say "soda," lest I seem like a rube. I kept saying "soda" for roughly the same amount of time I'd said "pop" in my formative years, yet when I moved back to a "pop" region three years ago I couldn't bring myself to resume the habit of my youth. I still say "soda."