I have heard from several agents that snippets work well when someone hasn't time to listen to a whole CD, especially if you cover quite a variety of material.

You MIGHT consider making a 'snippets mix' out of the best of your stuff as the first track on a demo CD, then putting the full length versions on as subsequent tracks. That way, the hurried promoter gets the quick picture, but can still listen at length later, if he has the time....

Just a thought...