I was searching for the best way to edit online content and Markdown was obvious choice. Until I saw what Medium has done. I believe that WYSIWYG is the only way. You still get emphasys on text but with no need to learn any kind of markup no matter how human readable it is.
On the other hand Medium's approach is tied to their visual style and design, it does not support many things I'd wish it would. Still, I'm rooting for WYSIWYG in the future.
[edit] Sorry, forgot to add that nevertheless this Markdown editor is impressive.
My problem with WYSIWYG editors is that I have never, ever seen one that does not end up adding messy markup that sooner or later becomes a liability when you want to switch to another tool, or find yourself in a situation where you want to hand-edit the document.
This is motivated by multiple blog platform changes etc. that all have left me doing messy filtering of exported data to be able to import it properly when moving my sites.
That's the appeal of Markdown for me. I'd rather add some custom filters to let me use some additional stuff in my own Markdown (which works ok since my additional markup worst case is just treated as plain text, and I can easily enough commit the code to turn it into "vanilla" markdown in the same repository as the content) than get tied into yet another format that messes with my content.
I only use WYSIWYG editors of any kind for content I expect to throw away now. E.g. reports at work that will have a lifespan of days to month is fine. Articles I want to keep an archive of for years to come, not so much.
But the web is not WYSIWYG, so you're really just editing text in a bespoke 'format' layered on top. Fair enough if that works for you, but it's important to recognise this and understand the drawbacks.
Textile / Textile2 is an interesting half-way house; less semantic in some ways that Markdown but balanced by more control over the output ( e.g. using h1 / h2 headings, ability to force paragraphs with p ) without wandering into tag-soup territory.
On the other hand Medium's approach is tied to their visual style and design, it does not support many things I'd wish it would. Still, I'm rooting for WYSIWYG in the future.
[edit] Sorry, forgot to add that nevertheless this Markdown editor is impressive.