Because this is an essay for National Honor Society, you probably want to reveal a little bit about yourself within it, rather than writing a dry and objective essay. (I assume this essay is part of your application.)
The "dominant" pilar to me would suggest the one I most easily excelled in. Then I would talk about why that pilar was my strength, and how the others were either byproducts of such a strength, or characteristics necessary to have this strength.
So I would probably choose leadership. I happen to be a pretty natural leader and always have been. I would write one paragraph about how my character affected my leadership ability, one paragraph about how my grades were affected by my leadership, and vice versa, and finally, a paragraph about how service is a natural by-product of being a good leader.
Do you see where you have a lot of room to make this essay personal, and that there isn't really one correct way to write it?