People might have sleeping problems for any number of reasons. Almost everyone experiences some nights where they just can't seem to get to sleep. Things like jet lag, noisy neighbors, or some kinds of illness can lead to sleeping troubles. Most of these people rely on over the counter sleeping aids to help them get to sleep in these cases.
There are basically two different types of sleeping aids that you can get at any pharmacy or department store. The first type uses antihistamines, the same stuff that you find in anti-allergy medication. The other type is based on some sort of herbal formula. Herbal sleep aids are becoming more and more popular as people seek out more organic methods.
Almost all over the counter sleep aids that are based on pharmaceuticals have one major downside. While they work well in making a person sleepy when taken, they sometimes work "too well" and make the person feel drowsy well into the next day. After taking these sleep aids, some people find it almost impossible to get out of bed even after 8 hours of rest.
People who try herbal sleeping aids usually find that they do not experience those same kind of negative effects, although they also find that they do not work as well. Valerian root is a common choice for herbal remedies, but you may need to try a few different types of herbal sleep aids before you are able to find one that really works for you.
As far as comparing different sleep aids goes, they are more or less all the same. Most of them use the same types of compounds to induce drowsiness (usually antihistamines). It's really a matter of personal preference and value.
You should consider that over the counter sleeping pills are not good for prolonged insomnia. If you have trouble sleeping often, you may want to consult a doctor.