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