I don't know that it is "the best", but CKEditor 5 is what we use because of how flexible and extensible it is. It has a plugin that can convert it to using Markdown instead of HTML.

Out-of-the-box, it likely isn't what you want, but if you learn how it and its plugin system works, you can make it what you want.

Their team also is fairly awesome - as we've twisted it to our needs, their support folks have always been there for us to not only answer questions, but even going so far as to understand what we are trying to do, and having their dev staff send us sample code to help us out.