Believe it or not, Gatorade is a great rehydration drink. They are one of the few companies that have done studies on their products and others (many companies haven't done studies on their own products; Gatorade has). They have been doing research for almost 2 decades, although I'm sure that lately they haven't had too do much. They are just doing tons of marketing. But really, Gatorade is a good drink pre, during, and post exercise if you want something cheap and simple; some of these other drinks and mixes are fine, but sometimes they have too much stuf for your body to effectively absorb and use in such a short amount of time. Combine it with a protein shake post workout to get more protein.
FHG