What makes some soft drinks have a stronger "fizz" than others?

I have drank just about every soft drink made. some, have a stronger fizz, than others. some contain their fizz longer, than others. the leader in the fizz department is Coke’s Diet Caffeine-Free Cola. the fizz lasts all day with the can open. why is this? do some contain a stronger amount of carbonation in their carbonated water or do the ingredients reduce the amount of fizz? maybe, the lack of sugar or sucrose in Diet Caffeine-Free Coke is the answer. Question: what makes the difference in the amount of fizz that one canned soda has over another?