I'm currently in the process of asking my professors for a letter of recommendation. I have 2 already set, but am having difficulty choosing for the third. My options are as follows:
-A professor who is quite old whom I took an undergraduate course with, he is somewhat known in his field and has went to a prestigious school. Offered to write me a recommendation letter, but he actually retired this past semester and isn't in the best health. Also I don't know him too well.
-A professor from the chemistry department (I'm a double major), who I also haven't taken many courses with but he knows me through word of mouth from the math department, is my chemistry advisor, and also knows me through research societies and such. He is young, but went to a prestigious institution and also offered to write me a recommendation letter. Does it hurt using one of my letters from someone that's not in a math heavy field?
-A very new professor who only got his PhD a few years ago, I've done a lot of work with him and taken a few courses. He was a visiting professor and just got on a tenure track, however he got his doctorate from a low ranked school. I heard it's not good to get letters from new professors?
-A professor I've taken numerous courses with (including 2 graduate courses). Also went to a somewhat low ranked school for his doctorate, and also seems to be more into the education side rather than mathematical research.
I'm curious to hear what you all think, thank you in advance.