Markdown is easier to write than HTML, in that you generally don’t have to close tags, and opening tags are much simpler (> to start a blockquote, for example). I find the closing tag key combination very awkward and disruptive to type (unlike the very satisfying and straightforward right-brace used in LaTeX). Markdown was specifically devised to convert easily to HTML but to be more easily readable and writeable. In recent months, I’ve tended to write in Markdown up to a certain point, then use iA Writer to convert the Markdown to HTML, and after that make any further edits to the HTML. That works quite well, I think.