He needs to be both and neither and one or the other. It depends on the group dynamics and the situation at hand.
If the group is endlessly planning, then some Captain is needed to get the game moving.
If the group is just starting out in a new world/campaign, then some navigator is needed to get the ball rolling.
If the group has a plan, a goal, and is implementing a course of action, then you need to be neither.
If your group has finished the campaign, and has spent the last two game sessions discussing the relative merits of serving girls of different races, and they havent even mentioned what they are going to do next, then you need to be both.
Well put, but this was asking for opinions. Not necessarily what works best when but what you feel provides the best game when done well.