You should get your letters from those who know you best and can write the best. For example, while my physics teacher in high school was awesome, I did well in his class, and we had a good relationship, my guidance counselor warned me he tended to write short ones. So I went with my AP Stats teacher who I also knew well and had a reputation for writing exceptional recommendations. If you have good relationships with all your teachers, try to go with 11th/12th grade teachers from a variety of subjects. If you are applying to Engineering, I would modify that and try to get two recommendations from math/science. I do think though what matters first and foremost is if they know you well and can write well and I would prioritize that over the subject they teach.