Every two years the National Resident Matching Program® (NRMP) publishes a program director (PD) survey that focuses on two main questions: 1) What factors do PDs use in deciding whom to interview? 2) What factors do PDs use in deciding whom to rank? Results of the 2018 Program Director Survey are available here.
So, as you approach interviews, if you're wondering what PDs want - by specialty - here are your answers. This document is extremely valuable.