Mediocre letter from professor or good letter from postdoc?

[braindump]

I'm having trouble trying to pick between two options for my third LOR. I already have 2 professors willing to write me letters with whom I have done research (a professor whose lab I've worked in for over a year and an assistant professor at another school where I had a summer research internship). I can't speak for how good the letters from these two will be.

For the third letter, I am getting mixed advice. At first, I was going to ask a professor with whom I have had a few classes; he knows me somewhat well, but only my academic ability. He wrote me LOR for the internship, but I don't remember it being particularly strong (he really only touched on my academics, but I've had another class with him since; maybe he'd write a stronger one this time?). Some people are telling me to skip the mediocre letter from a tenured professor and ask the postdoc with whom I've been doing research (knows me really well, would likely write a really good letter for me, has had his phd just over a year now). Others are telling me a postdoc letter would reflect poorly upon me, but I'm sort of leaning toward a strong letter vs an average one..

Any advice? 

[fuzzylogician]

Is it possible to have the letter from the postdoc be co-signed by the postdoc's supervisor, assuming one exists and is a tenured/tenure-track professor? That would give you the best of both worlds.

[braindump]

Is it possible to have the letter from the postdoc be co-signed by the postdoc's supervisor, assuming one exists and is a tenured/tenure-track professor? That would give you the best of both worlds.

 

The postdoc's supervisor is already one of the professors writing my letter. /: I guess I should have made it clear that the postdoc and the professor with whom I've worked for a year are from the same lab, but I'm not really worried about overlap between the two. I just work very closely with the postdoc and we're friends, so he knows me well and is always telling me that I'm a great lab member, so his letter would probably be strong.

Edited October 1, 2014 by braindump

[TakeruK]

I would have made the same suggestion as fuzzy but with the new information, I'm not sure how useful it would be to have two letters from the same research group, unless you worked on fairly different projects with the professor than the postdoc. But you did say that you are not worried about the overlap so it might not be a problem.

 

How about asking the postdoc and the postdoc's supervisor for their thoughts? If I were in your shoes, one option I might follow is to ask the postdoc's supervisor (also your supervisor right?) to include the postdoc's assessment of you in their LOR as well and then ask the prof that taught you to write you the third LOR. While research LORs are better than academic LORs, having 2 out of 3 research LORs is pretty good still. This is because I would be concerned that the postdoc does not have enough experience/reputation/respect (only 1 year after PhD, you said) to influence the admission committee. However, if this postdoc is a superstar that everyone knows their work then that might be a different story!

[braindump]

Hmm. Yeah, that's what I figured. Thanks for the input!