I agree with the comments on not taking energy drinks that basically have a bunch of stimulants in them, mainly because it can be dangerous. But don't discount sports drinks too quickly. During and after a hard bout of exercise you need to replace electrolytes, which water alone won't do. Plain water increases your blood volume and shuts off your body's thirst mechanism before proper electrolyte balance is achieved. You also need to replenish your muscles' glycogen stores, which water doesn't do either.