Diet pepsi. If you look at a can of diet coke and a can of coke zero, the ingredients and the nutrition values are identical. I've heard it said there is no difference between the two other than as a marketing tool to reach out to men who didn't want to be seen drinking anything "diet".
There is definitely a taste difference between Diet Coke and Coke Zero. Coke Zero tastes much better to me and I really don't have issues with the word "diet" being on the label. If I have to choose between Diet Coke and Diet Pepsi without the Zero option, I actually prefer Diet Pepsi but Coke Zero is better than either of those. I've cut down on all of that stuff, diet or not, to the point that I've only had maybe two or three in the past few months (outside of coke or ginger ale for mixed drinks but I definitely don't use diet for that
) so it's really not an issue anymore. One thing I have noticed since cutting back is that diet drinks taste pretty good when you're used to them but, when you've been off them for a while and then have one, they're actually not all that good no matter which one you're drinking.
It's kinda like wrestling a gorilla... you don't stop when you're tired, you stop when the gorilla is tired.