Hi Peer,
One thing to think about is most programs require students to take a broad business curriculum in the first semester/year of the program. So you will get exposure to finance, marketing, operations, economics before you select your major/electives.
I think most students going into the program know what they want to major in. In fact, you need to have an idea in order to write your essays (esp. the classic Why MBA question) but its not a decision you need to make from the start.
Like the previous poster asked, think about what function you want to do post-MBA and that should help you decide what classes you want to take, which will lead to your major/concentration. In fact, I would recommend looking at the major requirements of the school's you are interested in. See what courses are required for those majors and if any of them are of interest to you. That could give you a better sense of what majors could work for your post-MBA goals
Regards,
NP
Nikhil P. | Admissions Consultant | Veritas Prep