closed! ... though i haven't had any.
The most conversational interview, also the one I felt the interviewer got to know ME best, was the one that was the most closed, i.e. only personal statement and courses taken.
In completely open-file interviews I have to dig deep for that emotional stuff, talk about family issues, go into detail about ECs, research...most of which I don't feel has an important bearing on whether I'm academically qualified for med school or have the interpersonal skills to be a good doctor (it may help for getting a read on whether I'm a good fit for the school though).
In a closed-file interview I think you'd be able to make an impression as yourself rather than the sum of your numbers, ECs, letters, and personal statement. Ya know?