If your goal is to drop weight then avoid fruit juice altogether, fruit juices will spice your blood sugar raise your insulin level and get your body storing fat.
I avoid diet drinks because there are allot of studies that show splenda and aspartame to cause health problems, plus way to much sodium.
I drink decaf coffee and green tea and sweeten it with stevia.
When you crave fruit drinks make fruit smoothies with a
-cup of frozen fruit
the fiber from the whole fruit and the fat retard the sugar absorption so you do not get an insulin spike. Be carefully with smoothies because all the surface area will allow a high rate of absorption. Always eat smoothies after eating meat and salad.
You can tell you had to much sugar if you feel tired and a lack of concentration. If you feel tired after reduce the fruit and increase the fat next time.
Hope that helps