Ok, I've been wondering about this a bit. How about if we got a publication from a lab? It's not my current lab, but a lab I worked in in the past. Should I submit the letter from that? I've heard that if you got a pub, then you should def submit an LOR from that lab, otherwise it might look weird.
The problem is, my grad student wrote it for me and got it cosigned by the PI. I'm confident this student thinks very highly of me (he's mentored several students after me and has encouraged all of them to build off my project because he thought it was such a good project). However, I don't think he's ever wrote an LOR before, so I don't know if it would be "stellar". No doubt he said good things, but I'm not sure if he's experienced enough to make it sound amazing or anything. So basically, there's a good chance it's a stellar letter, but there's also a chance that it just sounds mediocre. Should I still submit it regardless? I'm not sure what he put in the letter, but I'm hoping he talked about how future students built off my project.
Note: I currently have 2 sci profs and 1 non-sci prof, as well as my current PI's letter. This would just be an additional letter to add to the stack. I have another PI's letter from a lab I worked in over the summer, and while I know he liked me a lot, I am almost confident his LOR is just "good" (<-- I only say this because he wrote the letter the day after I asked him for it; is that a valid assumption to make?)