I am a math M.S. math student who is looking for a transition to Ph.D in statistics/machine learning. I will be applying to Ph.D programs this winter, and I need to think about potential writers of my reference letters. My coursework consists of: Measure Theory, Functional Analysis, Smooth Manifold, Riemannian manifold, Probability (Measure), Algebraic Topology.
I decided to receive two letters from instructor of Riemannian Geometry and instructor of Probability respectively. Also, since I do not have a statistics background, I was planning to take Statistical Machine Learning and receive a letter from the instructor to prove my statistical ability.
Very unfortunately, the instructor has an Economics Ph.D with an affiliation in Business Department, and what's worse is that he is an adjunct professor with a heavy involvement in private sector. Should it be a good idea to receive a letter from the instructor nonetheless?
Alternatively, I can ask a letter of recommendation from my Analysis professor who taught me both courses in analysis for the past year (I did very well in Measure theory, but received B+ in functional analysis). Also, my most desirable place is Stanford, and he received his Ph.D in Math from Stanford. The only thing that I am worried is that I do not have a letter from a statistics professor.
I am very interested in hearing your precious advices. Who should I ask for my final letter? Thank you in advance.