I drink Coke Zero (sometimes the cherry) and Sprite Zero which I guess are technically diet soda. I do Diet Coke and Diet Pepsi too if that's all a store has. I have about 1 can every other day as a treat.
I always drank full calorie soda before I started my diet. Drinking the no calorie ones has had no effect on my weightloss or cravings as far as I can tell.