I have found Pepsi Max to be the best pop in its "Diet" category. It contains 0 calories, but it still tastes great. It tastes much better than the normal Diet Pepsi. It isn't quite as sweet, and that is a plus for me. I was a loyal Coke Zero drinker until I found this.
The extra energy boosters really do work. I use it when I need a pick me up (which is often when raising a baby) and it always works. This is impressive because I am usually immune to caffeine. It is not as drastic as the canned energy drinks, so you are not overly energized. It also has a much better taste than that...