Major means nothing in my opinion and my experience of applying last year and this year, all it matters that you have absolutely outstanding communicating skills and from what I have noticed most science majors including myself do not.
You have a higher chance of getting accepted into awesome schools if you major in humanities. If I could do it all over again, I would major in English. I doubt they are going to consider microbio major is much harder than bio, because then all the micro bio majors would be passed in favor of boichem majors which is much more intense at least at my school.