Sodas and fruit juices may taste great, but they're not good for your teeth. Both types of beverages contain a plethora of acids, some of which are more corrosive to your enamel than battery acid [sources: WebMD, Live Science]. Excessive consumption of soda or fruit juice can do serious damage to your enamel, especially if it's already worn. Therefore, consume these drinks in moderation, and rinse your mouth with water immediately afterward.
However, to be fair, the two types of beverages aren't equally bad for your teeth. Soft drinks contain ample amounts of citric or phosphoric acids, and one study determined that soda is 10 times more erosive than fruit juice. However, fruit juice erodes teeth more effectively than soda [source: Live Science]. Therefore, if your enamel is worn (or you don't want it to wear), it's probably a good idea to stay away from both types of drinks.