Previously Marked (http://marked2app.com), sometimes Vim, more often iA Writer because it blends markdown syntax with rudimentary formatting, and is well suited to editing text. (http://ia.net/blog/ia-writer-for-mac/)

Atom: https://github.com/atom/markdown-preview https://github.com/atom/language-gfm

and

Gitbook editor: https://github.com/GitbookIO/editor

Sublime Text 2/3. Great for code and markdown. I used to use Brackets because of the live preview for web development, but the simplicity and design (I use the "spacegrey" theme) makes it a pleasure to use. It has an unlimited trial or you pay $60, I believe.

I use sublime text 3 with following 2 plugins - Markdown Preview, for previewing in browser - Markdown Editing, great editing environment

I don't prefer online editors as don't like to see the live preview while I'm typing. But here's a good one dillinger

I can second the Sublime Text recommendation and add MarkdownPad (http://markdownpad.com/) for Windows.

I tried using Sublime text 3 for markdown but there was no significant syntax highlighting.

I use LightPaper and like it a lot. The features I like most are side by side preview and editor window and export to PDF and HTML. Previously I was using Mou but gave up after stability issues.

I can also vouch for LightPaper. The live preview is useful to check whether I messed up with my Markdown formatting somewhere.

http://clockworkengine.com/lightpaper-mac/

If I need something like live previews of my work as I am writing it, I just use light-table with the appropriate plugins.

Otherwise, any old text editor works for me.

Use <whatever> for editing and Marked for live preview:

http://marked2app.com/

I've used FoldingText:

http://www.foldingtext.com

Isn't the entire point of Markdown that you don't need a special editor for it?

Yes, but that doesn't mean some editors aren't more interesting or functional than others.

Sublime Text with the Markdown Extended plugin, or Vim, whichever is closer at hand.

I like Mou

http://mouapp.com/

Vim.

Exactly. Markdown, for me, is text, which you can read in the raw, and transform if you like.

Agreed. Here I treat nearly all text as text and edit in vim. That's why I like how simple and readable Markdown is.

Having a different editor for different text documents seems redundant to me. However I'll admit my two exceptions are using Xamarin for C# and ADT for Android apps.

if I want a live preview then I use http://stackedit.io. Most of the times I just use ST+Markdown plugins already mentioned here.

Haroopad is rather good on OSX. Give it a try.

Macdown is ok