What is a good question to ask an interviewer if given the opportunity

Who has been your favorite person to interview? What kind of questions do you like to ask?

Well if you're being interviewed, Is there any reason why you wouldn't hire me? Then you can address any concerns he/she has.

If you aren't being interviewed, I would say something like, What are you looking for in a person? Then you could use that knowledge in case you're looking for a job.