Hi there,
Thanks for posting. It's great that you are planning so far ahead and you seem to be very goal-focused which can serve you well. I admire that you are thinking this much about which activity to get involved with as related to b-school admissions. That said, I would also advocate trying to honestly/sincerely choose something that speaks to YOU, that you do have some passion for or interest in... either professionally (for your own development) and/or personally. Whatever that is... will work best for admissions, as they can see when you are genuinely interested in something you are involved in (through your essays and interview); it will shine through and that is more important than the actual choice of say which organization to get involved in. Additionally, if it is at all relevant, consider what involvement might further your long term career goals and aim for that. Good luck!