Diet Tips

Ive heard in passing that despite being labeled as diet, and having 0 calories listed under the nutritional facts, diet sodas arent all that much better than regular sodas.
Does anyone know how valid this is, and what the evidence behind it is?
With that example out of the way, the main question:
Does the same thing apply to lightly carbonated, sugar free energy drinks as well? And should someone dieting avoid indulging?