If you want results for your efforts, then what you really need is to understand the most critical aspects of the cover letter. The format is just one aspect. There are more details that you have to take into account. The content is the most essential point you have to bank upon. You might have a very crisp paper with nice format in it but it will not be helpful if you do not indicate the skills and credentials required for a certain job position. Of course, you need to possess the same essential skills, traits and knowledge. Thus, you must evaluate first your qualifications before aiming for the brightest cover letter format.
Make sure you choose a cover letter format that you feel most comfortable with. It should be something that could best express your personality but keeping it as formal as possible. Be wary of the details of the cover letter format. It must be clean and neat. It should provide the data directly. There is no need to be colorful or playful with the fonts.