Are diet sodas less harmful than sugary sodas overall, or just a different set of health risks?

How do I taper from drinking a 2-liter soda daily while still feeling satisfied at meals?

Do sports drinks hydrate better than plain water during workouts, or are they mostly sugar/marketing?

For a 2-hour endurance session in heat, is water enough or should I bring electrolytes/carbs, and what type is best?

What are the biggest competitive barriers facing emerging "healthier soda" brands against dominant incumbents?