Which one should I write?

So, I'm stuck between two things I want to write for National Novel Writing Month. The one I had originally planned was a Young Adult fantasy novel, which I had told my mom I was using. The other idea I had would be an extended version of a short story I wrote when I was 14. It's a lot darker, and kind of like Misery by Stephen King but not really. It's about the crazy fans of a musician. A lot of people liked the short story but said what happened in it disgusted them. I'm torn between the two.