Since I am raw vegan athlete for hydration I use coconut water. Coconut water is easy assimilate by the body, low acid, rich in natural electrolytes....and much more, but the important think is NATURAL!
Commercial sport drinks used carbs highly processed really hard to the body to assimilate, also, those carbs such as maltodextrin and dextrose makes your body spend a lot of energy digesting. So for me, the LAST thing I want when I am training/racing is spend energy digesting. Also something I notice is that with those commercial drinks, my body never assimilate the electrolytes, because in every Ironman I did using them I cramped and got sick. Since I started using coconut water or making my own drink that didn't happen again.
My favorite coconut water is Zico and that is what I have been using for training and racing.....For example, I just ran 14 miles, at 85 degrees out side and only use coconut water, with no problems at all!