Biochem and Physio are much harder (at least at my school) than Cell Bio and Genetics. So in retrospect, Animal Physiology would have been my choice.
But in the end, any course you will take will help a bit. But don’t expect that it will help a lot. In Med School, it is not so much the difficulty. I think anyone can understand the topics. It is more the volume. So you have to work almost all the time that you can spare…
Best or luck.