Mixed, lean FF. I've lived in Mississippi most of my life and hear White Southerners say "Coke" only when asked this question. Most people just say "soda" in everyday, conversational use. These terms (soda, pop, coke) have become identified as regionalisms to such an extent that people just say whatever they're suppose to say to appear "Southern" or whatever.
Personally, when referring to sweetened carbonated beverages as a category I tend to use the term "soft drink". I don't understand how a Mountain Dew or 7-Up could ever be called a "coke".
This is the only correct answer.