Where do you live and which one do you say?
I live in Cincinnati and say "soda" exclusively. Spending a few years out west and having friends from mostly California, Colorado and New York rid me of saying "pop" altogether. In Cincy, I'd say it's about 65/35 "pop" over "soda." I've not once heard someone say "coke" in a generic way referring to all soft drinks. That seems weird to me.
Amazingly, someone took the time to study, county by county, what everyone in the U.S. says:
Incidentally, my favorite soda is Diet Pepsi, though strangely enough at restaurants I'll order Diet Coke because that's just what most have. At the store, I'll always buy Diet Pepsi.