I may be off on the numbers but here is what my D’s GC had her class do (2017). She had to outline every Common App Prompt and write a draft for three. At that point, she decided which to start refining. I think it was a good process. The prompt she eventually used wasn’t what she thought she would choose at first.
Note: this method takes time. I get that we are now late September but it’s still good to draft multiple prompts.