I am a student at VCOM. It is a VERY flawed system. It is said that family, children, and spouses get priority. However, this usually means that you match in your very last choice. (extremely rural areas of virginia with no clinical experience to be offered, or even other states)
That being said, the only true criteria is your relationship with the faculty. Anyone in organizations who have a lot of positive interactions with the faculty will get their first choice no matter what. The system is based off of one or two individuals who often choose based on how much they like the student. Many students that have spoken out against faculty have gotten their last choice despite availability at other rotations sites.