You don't pick. They are all a potential key to your admission . Seek at least your congressman and both senator's nominations. Each nomination is a spot you are competing to win. Each MOC can nominate up to 10 candidates, but only one candidate will be awarded that MOC 's spot. Thus, you want as many moc spots as possible to try to win. You may be nominated by three MOC's, but not get an appointment from any of those nominations. In fact, that is likely true with many who have earned nominations, if not the vast majority.
Each nomination is like a lottery ticket, and the more you have the better your odds are of winning.