Should I ask a graduate student or professor for a recommendation letter?

So I’ve conducted laboratory research throughout multiple years at a lab. I’ll be applying to T20s schools and would like to get a supplemental recommendation letter for my application. However, I’m not sure who to ask. In my research position, I worked most closely with a graduate student in the lab, and therefore, she probably knows me the best. However, I’m technically working in the lab of a professor there, and maybe his position is more prestigious and meaningful in a rec letter.

Would it be better to ask the graduate student or the professor who runs the lab? Would AOs view a recommendation letter from one person more favorably?

Better to get it from someone who knows you well and specifically describe your responsibilities, skills, etc.

A generic “this person worked for one of my grad students and I’m told he/she did well. I met her/him a couple times - seemed nice” letter doesn’t carry much weight.

For admission, the committees want to see a letter from someone who can write about you as a student - in other words one of your current or recent high school teachers. What the PI and grad student might be most useful for right now, would be in helping you formulate your application list if you are interested in continuing in this specific area of study. Even if you aren’t interested in that field any more, their letters will be useful when you look for job or a position on a research team at your new college/university next fall.

@happymomof1 The OP said this letter would be a supplemental LOR not a replacement for a teacher’s LOR. Many colleges do accept a supplemental LOR that speaks to the applicants abilities/talents outside of the classroom.

To the OP, I would ask the person who knows you best to write it which sounds like the grad student…or perhaps if they are willing both the professor and grad student can sign the letter.