Ranked in these QuestionsQuestion Ranking
Pro Supports multiple Markdown dialects
Unfortunately, this is a global setting for save (it can open any dialect)
Pro Immediate Markdown rendering and preview
Texts immediately renders the formatted Markdown as you are typing it inside the text box. It's quite similar to a WYSIWYG editor.
Pro Imports and exports many formats
HTML, Word, TeX, PDF, ePUB, OPML.
Pro Works on Mac OS X and Windows
Con Overwrites standard Markdown
Editing a preexisting Markdown document overwrites standard markup in it (for example, interpreting headings marked with leading "#"s and rewriting them with a trailing underscore line), adds extra blank lines between all paragraphs, and adds extra spaces at the head of unordered-list items.
Con Spell checking is not activated by default
There's a built-in spell checker which is not activated by default and is quite hidden.
Con Limited choice of built-in themes
You can download the CSS for these themes and create your own, but would be nice to have more flavors (e.g. GitHub)
Con No word count in older versions
Word count is present in Texts 0.21, at least.