Do your best to stay away from soda. All sodas are sweetened with lots of sugar. The more you can cut out of your diet the better. Also, diet soda is still soda. It may not have as much sugar, but it has other chemicals and components that are not good for your body either.
If you drink a soda, counteract it with a glass of water. Remember, caffeine dehydrates you as well. Decaffeinated sodas still have caffeine in small amounts as well and just as much sugar, so they are not much healthier either.