I'm a relatively old student (29F) Currently applying for PhD positions in ecology, mainly in Europe.
Many applications encourage adding 3 letters of recommendation. I have two solid ones related to my MSc thesis topic. I'm on the fence about what to add as a third reference. I worked as a research assistant in various projects. Most of the time, I worked alongside PhD students. They know me well and could write informative statements. The profs who are running the projects haven't really worked with me, even though I was officially hired by them.
My question is: Should I go for a general letter from a prof who doesn't know me, or go for a statement from A PhD student who can write better, more informative things about how I work? How important are the letters anyway?