As this is specifically for markdown editors, i’ll skip talking about anything else.
If i’m writing pure markdown, I use a mixture of https://caret.io/ and https://github.com/wereturtle/ghostwriter, depending on what i’m doing. Doing quick site edits or whatever i’ll use a proper editor, but for just getting on and writing content for Hugo, these are great!
Writing other things often requires different editors, and looking back at this thread, most people have taken this as a ‘what editor do you use’, which IMO is a fairly different question