I find that the nylon thin pick has a much faster action and a more clap crisp sound to it on the strings.  Thick picks have a more dull sound and they rotate on me where as thinner picks do not seem to rotate so quickly, and being that they are thin you can really get some fast strumming patterns without the pick flying out of your hand.  I have ordered Dunlop Nylon Picks 38 millimeter for my Classical Nylon Guitar because the strings are much larger and they make picks rotate even faster in your hand; so the thinner the better.