I worked with a professor (let's call him "Prof P") at my home institution for an REU, then the following spring semester (~8 months in total). I didn't make much progress on the project for a number of reasons, but mostly because I was essentially working on it alone (no other grad students) and Prof P couldn't help (the project was centered around a circuit, and he admitted that he didn't have much knowledge of modern electronics). I asked him for a LOR for applying to physics graduate schools. He said that he would write a good one, but he wasn't sure why I didn't do well with him. I explained to him that I was kind of thrown into the project with little guidance, and floundered as a result. He responded by saying that the project shouldn't have been difficult for me to do (even though he couldn't figure out what was wrong with it) and that another student who worked on it after I left got it working in ~2 weeks. He claimed that it was an easy fix (and that the project wasn't difficult in the first place), yet he wasn't able to explain to me how the other student got the circuit to work (go figure). The REU was basically my first research experience, so he thought that my performance could be chalked up as "immaturity" (at least that's better than incompetence!) Regardless, he said that he would write a good letter and wouldn't mention any of the above. He seemed honest and sincere, so I think I trust him. Since his recommendation would just be "good" and not "glowing," I was thinking of asking another professor ("Prof T") who I TA'd for (he enthusiastically offered a letter when I finished teaching his class). Here's the issue: My work with Prof P was for 8 months. My only other research experience is ongoing (and with 2 other professors), but I've only been working on those for the past 3 months. Those 2 recommendations should be very good, but one of them isn't in the physics department (it involves designing amplitude and frequency modulated RF pulses for use in MRI, and simulating the resulting nuclear magnetization in Fortran). In the other research project, I'm not directly working with the professor (I'm working with a grad student of his), but I also TA'd for that professor, in which I communicated with him often. Also, I didn't interact all that much with Prof T, so I think his letter would be pretty brief and would solely focus on my communication skills. Will it look really bad if I don't get a recommendation from Prof P, since that was my longest research experience? I would think that 2 good research LORs and 1 teaching LOR would be ok, but I'm really not sure. Prof P and I never really got along or communicated very well (he sometimes was rude in emails, one time implying that I was faking an illness), but I got along great with the 2 other research professors and Prof T. I don't want Prof P's possible mediocre letter to weigh down my other 2 great letters, but I feel like not getting a letter from him could be just as bad (a bit of a catch 22, eh?) Any advice would be greatly appreciated! Edit: Something I just thought of: would it really be that bad if I didn't get a letter from Prof P, since graduate schools might see my continuation of the project in the spring as evidence that Prof P liked my work enough to still want me to work with him?