Best bet is to look for soda made with pure natural sugar rather than high fructose corn syrup. Even Mountain Dew has a version like that called Mountain Dew Throwback, I do prefer it to the regular kind except I haven't found it canned and boxed yet I think they also have Pepsi Throwback which is the same thing except not mountain dew.

Other then that there are better artificial or calorie free sweetners than what they put in diet soda that aren't nearly as bad for you.

I think even sugar free energy drinks typically use better artificial sweetners, I've gotten them a couple times by accident and figured I'd get nauseous like with diet soda, but I don't seem to have that issue with those so I think it could be they use different sweetners not entirely sure though.