What is the most carbonated soda?

By definition all beverages called "sodas" (or "pops" or "soda pops") contain dissolved carbon dioxide that escapes as a gas forming bubbles when served. This is why they are called "Carbonated Beverages".

There are several other types of "carbonated beverages" that are NOT "sodas", a few of these are: sparkling water, sparkling cider, cold duck, beer, champagne.