When looking at buying one of the sports drinks products that are out on the market, you'll want to take into consideration a couple of factors.
The biggest point to consider is how intense the activity you are participating is. If it is very intense in nature and you will be burning a great deal of calories, you'll want to look for one of the products that contains a higher level of carbohydrates. This will ensure you have plenty of fuel to keep the muscles working.
Next, when looking at the products, make sure to take into account if they have any extra added ingredients. This could be ingredients like caffeine, protein, and any added vitamins.
Additionally, you'll have to take into account how long you are going to be exercising for as well. If it is a shorter duration session, you may not even need a replacement product at all and would do quite well with just water. Then, for moderate length activities, one cup or so should serve you effectively, and finally, for those who are going longer than an hour and a half, two cups or more will likely need to be taken in to keep up with the needs of your body.
Make sure you do try a couple of different brands as well since they will vary in taste and how well your body tolerates them. If you find you get cramps easily while exercising, you will really want to plan your drinking strategy wisely in order to avoid suffering a decrease in performance.