My initial reaction is to say 'coke', but that gets filtered through years of learning that if I call it that I'm probably going to have an irritating conversation and the word 'soda' comes out of my mouth instead.. In my home state, there was some geography/class playing into it, so calling it coke might get viewed as backwards or country depending on how polite the other person wanted to be. But after moving to California, and dealing people acting like I'd grown a second hand that was speaking in tongues if I call it coke, I try to avoid any such regionalism.