I’m assuming that you’re targeting a technical audience since you’re posting here. I don’t want to sew any bias into the thread, but I’d be surprised if most people didn’t say that they prefer markdown.

That being said, I’ve been using dropbox paper for note taking which supports markdown and I’ve been loving it. The other tool I use for quick notes is jrnl.sh

Good luck building the project! Definitely do a Show HN thread when it’s finished.