i think it all depends on your school and which one they make more difficult. My school only offers biology or biology with an emphasis in microbiology... and each is hard with different reqs. Bilogy is like an umbrella making sure you take a field class, lab courses, etc... microbio doesnt care about the field class and focuses more on microbio classes. I would ask your school
Again, as long as you fulfill your pre-reqs for school, you major doesnt really matter
My school offers both, and there are pre-health students in both. The B.S. in Bio degree seems much more difficult to me, alot more upper level courses and independent lab courses fill up my schedule whereas the biomedical science students get ALOT more electives. We both come out with all the pre-req's but theirs are built into their schedules and I have to cram them into mine.