Who should I ask?

[biggspc]

I need three LOR's for most of the schools I'm applying to. My favorite program asks for at least 2 recommendations from "college instructors." Now, I've already asked one of my professors as well as a former employer. The third person I'd like to ask is a research scientist at my school who is supervising my in an independent study. I believe, he also teaches a course, but I've never had a "true" course with him. Is he an appropriate choice or should I ask another professor?

[Quant_Liz_Lemon]

My strongest rec letter comes from a prof that I've never had a class with. He's supervised my research, I've TAed for him, and I'm the research coordinator for his lab. In my experience, adcoms want someone who can comment on your ability to do research.