Bro, the first question that needs to be answered is not what sleeping pill you need - but why you aren't sleeping. One thing I have noticed as a pattern is that some people are very affected by certain foods and substances like sugar substitutes.
Asparteme is a phenyalanine (spelling?) molecule splice onto a glycine molecule. L-phenyalanine turns into tyrosine then into noradrenaline in your body. Noradrenaline is the brain chemical that makes you feel awake. So, a lot of people who have a diet soda 4-6 hours before bedtime can't sleep a wink cuz they just jolted their brains full of noradrenaline.
(BTW, melatonin, GHb, and Benadryl are the three best sleep aids.)