Don't you wanna see the school before calling it your top choice?
Instead of answering which school is your top school, I think you should say that your top school will be chosen from the schools you've applied and interviewed at. They you will come up with decision of which one is at the top depending on what you see during the interview and of course what you hear from other students. Jest mention that you seriously conceder them.
I told my interviewers that after the interview, I will be doing the same thing they will
go over the list and compare school to school, pros to cons.