Use sales letters after you have sent letters to personal friends, business acquaintances, and recruiters.
The letter to friends is like the grand opening for a store. It's the first step in your marketing campaign. It announces your candidacy to the world and launches your job search.
Write to recruiters second, because they are in the employment business. Although they don't work for you, and they fill a relatively small number of positions, they match candidates with employment opportunities all day long. There just might be a fit.