The worst thing about coca cola and pepsi is the phosphoric acid which is fairly strong and needs to be labeled as corrosive to be transported anywhere (even for food). It will cause you more tooth problems than anything.
The verdict on high fructose corn syrup is up in the air still.
Notice things like sprite do not contain phosphoric acid but citric acid which will not bother your teeth at all comparatively. However, none of these drinks contain caffeine which is what a lot of people like when they drink soft drinks.
Also, caffeine is not bad for you at all except in large amounts or in the case of specific issues like allergies or high blood pressure. As far as I can tell it has not been labeled as any type of carcinogen either.