A structured interview is where a person conducting the interview will ask a series of predetermined qu

A structured interview is where a person conducting the interview will ask a series of predetermined questions in order to gain more information about the person who is being interviewed.  This type of interview will use a standardized process of inquiry, is quantitative by nature, is easy to replicate, and is also sequential. On the other hand, the unstructured interview does not use standardized questions or have any specific set of questions for the individual being interviewed. It will instead involve questions that are more about context and purpose. The interview process is typically flexible, relies on spontaneity, and is more qualitative and descriptive by nature.

I think that you will get a more authentic response using the unstructured method just because of the fact that it is more spontaneous and requires the person being interviewed to be more of themselves since they do not have a planned response for questions normally asked during the structured interview process. 

Reference:  

Blog, Formplus. “Structured vs Unstructured Interviews: 13 Key Differences.” Https, www.formpl.us/blog/structured-unstructured-interview.