1. SA DVM (2 years) - Worked 10-15 hours a week under her for 2 years at a SA clinic
2. LA DVM (a few months) - Spent 4-12 hours a week shadowing this vet during the summer. He was an LA vet who drove around to farms, so all of those hours were sitting DIRECTLY NEXT TO HIM AT ALL TIMES. I continued to shadow him past the LOR stage and we're now very close, but at the time I would still say I knew him better than LOR writer #1 because of the situation.
3. Cheesemaker - Okay this sounds weird, but this woman makes goat cheese and milks a herd of goats, and I did an internship with her one summer that was about 10 hrs/week. I milked for pay the next summer, and do so again this summer! We are very close and she's been an outstanding mentor for me. And she really wanted to write me a letter. 😉
4. PhD - my undergraduate advisor who taught one of my classes and supervised the above internship. We spent less time together, but he knew me best as a student/in an academic environment
5. DVM/MS - My PI at a research lab I worked at for the summer during apps. I continued to work there past that date, but I had only know her a few months, and spent way more time with the other lab jockeys than her, but she wrote me a good letter, I believe. She's also sort of a big name in her field, so I thought it'd take advantage of the opportunity.
I took advantage of having as many people vouch for me as possible, but I think I could have gotten by with fewer. Also it really did range how much time I spent with them, but the letters than I think truly carried the most knowledge of who I was as a person were #2 and #3.