advice needed on who to ask for third rec!

[salome]

I'm applying for Master's degree programs. At this point, I have a former professor (from the area in which I majored, which isn't totally related to the degree) and a former employer who've agreed to write letters of recommendation. The former employer is from a research organization that is directly relevant to the degree programs to which I'm applying. For my third recommendation, I'm torn between asking another person from my former job at the research organization (because it's so relevant to the graduate programs) or my current supervisor here in the Peace Corps. I feel like the latter would give the letters a more well-rounded feel and I don't want to be repetitive with two letters from the same job. However, I'm not sure how my supervisor in the Peace Corps program can really speak to my academic ability to perform in this type of graduate program. Oh, and another professor is an option but she would be from an unrelated discipline (again, from my major). Suggestions? Thanks!

Edited September 2, 2010 by salome