Keep it nice and simple - don't try to be funny or clever. Tell them that you have researched the job (and make sure you have!) and you believe that your skills will make a valuable addition to the company, and take it forward, and you'd like an opportiunity to try and do that.
A number of years ago I came to the conclusion that I didn't want to work for anyone who asked that question. If you haven't met the other applicants how can you argue you are the best candidate for the job?