After your interview, from what my interviewer told me, I think that all the factors are meshed together. It's just that your interview "score/evaluation" is added into the whole pot of criteria. At the University at Buffalo School of Dentistry, my interviewer said that the committee will meet, consider the intervewer evaluation, add the score into their huge formula (which includes GPA, DATs, extracurrics, observation exp., desire, motivation, personality, etc.) and churn out a number. There are cutoffs for reject, alternate status, or accept.
Hence, for people with lower GPAs interviews are more "make-or-break" in importance to their acceptance odds.
For the bulk of interviewees, I think they should know that being invited for interview means you're pretty safe in terms of academics; so the interview is important for them too- it adds that entire human dimension to their applicant "formula" and it is the factor that separates them from other applicants who are identical on paper.
So to answer your question I would say it's the interview that's most important.