Actually, the best drink to take on a hike is a Nalgene bottle ($10; www.nalgene-outdoor.com) filled with Doles Pine-Orange-Banana Juice. Freeze it, then stick it in the pack. About the time you are REALLY thirsty and it is REALLY hot, the stuff will have melted to a lovely slushy consistence. I love that stuffand its actually a pretty good sports drink, with some natural sugars, a good dose or carbs, and electrolytes such as potassium.
Anyway, thats just me. But Pine-Orange-Banana has fueled me on many a hike or ride.
Otherwise, I suggest going for a mix of sports drinks and water. Sports drinks certainly have their place, but these days theyre over-hyped and over-sweetened. One option is to pack a bottle of sports drink in your pack, toss in a bottle of water or a hydration bladder full of water, and alternate when you get thirsty.
And, given the nationwide heat wave, your question presents a good time to discuss the dangers of drinking TOO much. Thats rightyou can easily over-hydrate. The condition is called hyponatremia, and it happens when you pump so much fluid into yourself that you literally thin the sodium in your blood that helps keep the machinery firing. You may experience nausea, muscle cramps, disorientation, slurred speech, or confusion. In really severe cases, seizures may occur, and even death! Its commonly seen at ultra-marathon events such as the Ironman in Hawaii, and in places such as the Grand Canyon. Treatment can include eating salty foods such as potato chips, or drinking some sports drinks that have sodium.
So there you go. Cheers!