Answer:
The best alternative is water. It keeps your body hydrated well and in doing so keeps your heart pumping better and it is easy to process on the kidneys, pancreas, and liver. Water is the one drink that does not cause cavities, at least as it relates to bottle water, processed/filtered water, and most (not all but surely most) household taps.
The Gatorade drinks, Power-ades, and other drinks that scream they are the best because of the so-called "electrolytes" are actually the worst you can put into your body. Low-sugar/no-sugar drinks normally have saccharine or saccharine-like artificial sweeteners, which can cause migraines and in the past it was believed to be a carcinogen. The Center for the Science in Public Interest (CSPI) wrote a report to the National Toxicology Program (NTP) in 1997, claiming that by removing saccharin from the list of possible carcinogens.
Sufficient evidence of carcinogenicity in animals (multiple sites in rats and mice) and limited or sufficient evidence of carcinogenicity in humans (bladder cancer). It is prudent that saccharin return to the carcinogen list until there is enough research with conclusive evidence showing saccharin to be safe.
FYI: It is important to note that Saccharin is a part of the sulfonamides. If someone were extremely sensitive/allergic to sulfa antibiotics, there is a risk of allergic reaction to consumption of food or drink products that include Saccharin. The list of allergic reactions include but are not limited to: headaches, breathing difficulties, skin eruptions (welt-like hives on the skin), and diarrhea.
It is a reasonable belief that the saccharin used in some infant formula products can possibly cause irritability and muscle dysfunction. There is no hard proof of this fact; however, there is documentation to reduce or remove saccharin from the diet for infants, children, and pregnant or nursing mothers. The FDA cannot limit the use of saccharin in formula for infants without the necessary research to prove or disprove the safety or danger of the product for certain. As a mother, I would not be willing to take the risk of including saccharin in the diet of my children or myself especially if I were pregnant or nursing. Besides, saccharin products are a migraine trigger for me so I stay away from it either way.
EDIT: For many athletes, drinking too much water can be an issue and although the sugar content is high, it replaces the electrolytes that your body NEEDS.
From About.com, "Athletes sweat heavily, losing both water and electrolytes. Water intoxication and hyponatremia result when a dehydrated person drinks too much water without the accompanying electrolytes." Maybe Gatorade isn't the ideal drink around the dinner table, but don't worry about the excess sugar when you are using it to recover from exercise or a sporting event.