I would echo the above. Of the three schools I visited (Duke, Kellogg and Booth), I thought the Duke visit was the best. There were probably about 10-15 prospective students there, some interviewing some just visiting, and 2 or 3 ambassadors. While with the size of the group you couldn't have a 1 on 1 with any of the ambassadors for too long, I think they did a good job making sure that all the prospectives' questions were answered, and they seemed genuinely friendly and excited about Duke.
Regarding the use of students as interviewers, I'll admit the Duke website isn't as clear as it could be:
Quote:
During the interview you will be asked a variety of questions that will give you the opportunity to present your background and interests to a member of the admissions committee.
At Duke, the students who do the interviewing actually are members of the admissions committee, but I could see how the webpage could be misleading. Regardless, I wouldn't worry about it, the students have been trained, and you have the same opportunity to present yourself as if it were an admissions officer. It seems like again you had bad luck with your interviewer, mine was incredibly friendly and the interview was very conversational.
All told, you certainly shouldn't choose a school you don't feel like you would enjoy attending, but if possible I'd try visiting again. Or, if you're admitted, Duke runs admitted student events in various cities, so I'd suggest attending one of those to get a feel for potential classmates.