The majors with the greatest congruence with med school pre-reqs include: biology (and any of its subfields including neuroscience), chemistry, biochemistry, chemical engineering, biomedical engineering, and, at some undergrads, public health.
There isn’t an optimal major for med school. A bio major can get you to med school, but so will a English lit, theology, classics, mathematics, gender/ethnic studies, computer science, or music theory major.
Major in a subject that you a) enjoy and b) will do well in.
It is also important to think about your Plan B when choosing a college major. Admission to medical school is quite competitive with only 38% of applicants gaining an acceptance last cycle. Every pre-med needs a Plan B.