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:
http://www.popvssoda.com/countystats/total-county.html
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.