I am confused about the alcohol found in most conditioners. What does cetyl alcohol, stearyl alcohol, and the like do to one's hair?

I was under the impression that alcohol dries out hair...

Is one type of alcohol better than others? If so, what is the difference between them and what do they do to enhance your hair?

And what is polyquaternium? Is a certain number of polyquaternium better than others? (i.e. polyquaternium-72, or polyquaternium-4)

If I had a choice in getting conditioner with an alcohol or one with polyquaternium, which should I get?