Huh. Interesting. It is obvioulsy up to you but I don't think anyone cares from the standpoint of what your resume/diploma says.
If this involves a certain group of classes/courses - I would pick the best professors and what's of most interest to me (look at the classes). However, I would not subject myself to torture to get one or another concentration/specialization. What matters the most is can you find a job after graduation and what will help you with that?
It is really what you want to have your diploma say so that if you are switching industries and going from Finance to Marketing or General Management, you can claim on your resume that your MBA is in Marketing and therefore they should pick you.
P.S. Nobody ever cared to check or even know my GPA from BSchool or what concentration it was in.
Though most of my bosses have not had an MBA so they were very impressed with my resume to start with.
PPS Many schools do not have a concentration
PPPS Some schools will ask you what you want your concentration to say
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