What common app prompt to choose+ what to write about?

Very honestly, I don’t think you should follow those CommonApp prompts Personally I feel those prompts are vague and don’t really give you the answer to your story. My advice for you as you tackle on your essay is that you write your story based on what you what the college to know about you. Don’t follow the prompt and write your essay and once you’re finished with it, then see what prompt it matches the most with. As for a good topic, I would say something that has really good meaning to you, basically making you into the person you are and somehow connecting it to how you are prepared for college and what you want to do later in life. Hope this helps!

If none of the more structured prompts are speaking to you, I'd recommend #7: "Share an essay on any topic of your choice. It can be one you've already written, one that responds to a different prompt, or one of your own design".

I would also recommend not trying to structure your personal statement explicitly around "something you've done". The personal statement is an opportunity to showcase your personality and beliefs, not just regurgitate one of your ECs. That doesn't mean you can't mention one of those activities, but the focus should be on you—your growth as both a person and a student. One approach that can be helpful is to think of a challenge you faced doing one of your ECs. What did you learn? Who helped you? Why does this challenge matter and how did you overcome it?