this is a sleeper question during interviews.
I cannot answer this question for you. I can only give you some guidance. I know what makes me unique, but i have no idea what makes you unique. Only you have the answer to that.
1. Make sure you do not say that you are better, more knowledgeable, more competent, or better qualified than the other candidates. Like my relationship to you in my lead in sentences, you have no idea what makes the other candidates unique. You have no knowledge of their qualifications. As soon as you start to state that you are the better qualified candidate, someone else will have much better credentials.
2. Instead focus on what your main attributes are. Attributes are the key. without comparing yourself to other candidates, state simply that you are unique because: (and then start listing your uniques in sentence format)
If they insist on a comparison, You can use this one:
Look, I really do not know anything about the other candidates. I am sure they are highly qualified or you would not be considering them along side of me. I am honored to be in such company. However, it is hard for me to imagine anyone wanting this position as much as me.
These of course are examples. You will have to think about all the interactions you have had with teachers, parents, employers, and friends to find out what your attributes are. Perhaps you are the one everyone comes to for advice or to settle a disagreement. Perhaps you are the go to guy for difficult tasks.
You can even ask people what they think your attributes are. (risky but fruitfull).
Make your list, then pick out what are your strongest.
A good mix would be attributes related to:
1. Ethics (work and honesty)
2. Team work
3. Problem solving and creativity
4. That you want the job.