None. The end.
Not all contain aspartame. Even still, it's bad not because the supposed cancer risk (which isn't accurate) it's because research is starting to show our bodies react to artificial sweeteners in a very similar was as to sugars. Plus, they maintain our mental conditioning for very sweet drinks.
Then there's all the other crap they put into soda.
Take a water bottle everywhere you go, refill it with water. That'll help curb the soda habit.