Looking back on your last position, have you done your best work?
To cover both possible paths this question can take, your answer should state that you always try to do your best, and the best of your career is right now. Like an athlete at the top of his game, you are just hitting your career stride thanks to several factors. Then, recap those factors, highlighting your strongest qualifications. Why should I hire you from the outside when I could promote someone from within? Help him see the qualifications that only you can offer. Example: “In general, I think it’s a good policy to hire from within – to look outside probably means you’re not completely comfortable choosing someone from inside. “Naturally, you want this department to be as strong as it possibly can be, so you want the strongest candidate. I feel that I can fill that bill because…(then recap your strongest qualifications that match up with his greatest needs).”