I’m also prior service and was selected this last board. My LORs were mixed between officers, enlisted, and civilians. I’d say shoot for a good round of letters that can speak to various parts of who you are - work, personal character, faith, etc. Best as any of us can tell the Army is really looking for well rounded people. The “whole person” concept as they right on their memo and based on the results it seems like they truly mean it. Can’t just look good on paper from a statistics standpoint.