Your answer needs to be short, sweet and to the point. It needs to tell your prospective client exactly what makes you the REALTOR they want to work with; someone they can trust, someone who work hard for them, someone who will look after their best interests.
Now comes the hard part, what sets you apart? Your customer service skills -- what does that mean? Your communication style -- what does that mean? You are easy to talk to -- what difference does that make?
Ask your past clients, or friends, that like you :-) the reasons that they chose to work with you and why they believe you are worthy of their trust. Write these down and see if there is a common thread. Find the 3 top reasons, and then formulate a speech, a brochure, a statement for your website etc which tells your prospective clients how you are going to help their dreams come true...better than anyone else.