Who should I choose?!

[emmakroloff5]

I am trying to get all of my letters of reference together as early as possible and am struggling a little bit with who to ask. So far I have set in stone the MD I work for as a medical assistant to show my clinical experience. Academically, I had a 3.4 GPA and I know this is on the low side. I didn't have an insanely great relationship with any of my professors but would be asking the one I had the closest relationship with. I got a B+ in his "Advanced Anatomy" class and also traveled to Nepal and shadowed in a medical clinic with him. I also have the option of asking a teacher who absolutely loved me, but was a freshman year teacher for a Bib Lit class. I was also a division 1 athlete throughout my collegiate career and was going to ask my cross country coach as I know he can speak well of my work ethic. Finally, I was an avid volunteer and could ask my mentor who could say great things (but this volunteering was not medical). Amidst all the mumbo jumbo I am essentially trying to choose the best three candidates and also would like to know if I should start searching other places (I have heard and read on here it is important to have PAs).
1. Doctor I work for
2. D1 coach
3. Science Teacher?
4. Volunteer Mentor?

[slanderousion]

I feel Volunteer Mentor seems to be the best choice!