sugar accelerates the depletion of vitamin B which will make the hangover worse. diet coke doesn't have sugar so you can still have the benefits of drinking alcohol with a carbonated drink if you don't have a lot of liquor to drink.
i don't want to sound like im talking down on anyone. but from what ive experienced every underage drinker loves captain and coke. and i did too. then you get REALLY sick of it by about 22.