Less sweeteners
Both are obviously bad for your health, but it seems the lesser of the two evils would be Diet Coke, simply because you only have one sweetener and its adverse effects to deal with, while Coke Zero gives you two different sweeteners with adverse effects from both to deal with.
I can't explain it, I just feel worse after drinking Coke Zero, and I feel better after drinking Diet Coke. Coke Zero tastes better than Diet Coke, but since I feel better with Diet Coke, I stick with Diet Coke.
it not as sugary
its good little bit because coke cola make it sick in winter and spring