I am applying for physics graduate programs. For context, the graduate programs I am applying to require three letters of recommendation and most of them do not allow more letters.
I have several options for graduate recommendation letters. I plan to send one letter from my current research adviser and one letter from my research adviser from the REU program I did last summer.
For my last letter, I can either request a rec from my research adviser from another summer research program I did two years ago OR from a professor I have a good relationship with who taught an undergraduate class in quantum physics my sophomore second semester. Which final letter writer should I choose?
The reason I am hesitant to go with the professor is because I am not sure his letter will add much. I have a 4.0 GPA and I have no research experience with this professor, whereas I believe the research adviser from my summer research program can write a strong letter and can discuss my abilities to do research.
I have taken additional physics classes (and some graduate courses), but I did not develop a close relationship with the professors and those professors can at best say I got an A in their class and was an engaged student.