The easy answer is that you are the best person for the job. And don't be afraid to say so. But then back it up with what specifically differentiates you.
For example: "You should hire me because I'm the best person for the job. I realize that there are likely other candidates who also have the ability to do this job. Yet I bring an additional quality that makes me the best person for the job--my passion for excellence. I am passionately committed to producing truly world class results. For example..."
Are you the best person for the job? Show it by your passionate examples.