I am an undergraduate senior applying to graduate programs in Computer Science (with math-y specialties, such as Machine Learning and Data Science), and am trying to figure out who the best people to ask for recommendations are. I've already asked a professor whose class I did well in and tutored for, and a former manager of mine who has a PhD in the same field. As for my third one, I'm thinking about two options:
a) My high school math team coach: Math Team was my life back in high school, and I feel that my coach is one of the few people who truly knows how much I love math and learning in general. In addition, he also has a PhD in the field (in fact, he and my former manager did their PhDs together!). The only downside to this that I can see is that he is not familiar with my work in college, but I think the fact that he knows academia and my own academic potential makes up for that. Unfortunately, I have read that recommendations from high school teachers are generally looked down upon, so I don't know how great that would be.
b) My current Machine Learning professor: Machine Learning is what I really want to do, and a recommendation for someone who actively teaches it and is involved in the field would be great. However, I am worried that since the semester is not over yet, he may not have an accurate feel for my academic ability (although I have been doing well in the class so far). Additionally, I do not know him very well - I have been talking to him a little bit about grad school and advice for a career in ML in general, but I don't know if that is enough for him to write a strong recommendation with.
Given this background, which recommendation do you think would be stronger?