Would it be better for me to write about a specific incident in my life (not life-changing, but clearly shows character), an activity that I’m really involved in and passionate about, or something wholly unrelated like choir or running? I can see the pros/cons of each but I’m having trouble choosing one.
Write whichever one will make the best, most memorable story. The best essays start with good stories; you can pull plenty of messages, themes, and qualities out of any great story.