Slow release (low glycemic, complex) carbohydrates such as vegetables, whole grains and beans are generally the better choice for two reasons. First, they will not spike the blood with too much sugar so the body is not required to release a lot of insulin in a short time. Second, they contain a lot of fiber which is necessary for overall good health. Fiber helps prevent colon and rectal cancer. It also binds with oils (fats) and eliminates them from the body.
Simple carbohydrates (especially high fiber fruits) are good if you need a quick energy boost; for example, before a short duration athletic event, or when you are tired but have to keep working a little longer. Otherwise, simple carbohydrates are best consumed in conjunction with, or immediately after, other foods – e.g., proteins, fats and complex carbohydrates. This will help balance the amount of sugar released into the blood.