When comparing Texts vs Zettlr, the Slant community recommends Zettlr for most people. In the question“What are the best open source Markdown editors for UNIX-like systems?” Zettlr is ranked 9th while Texts is ranked 29th. The most important reason people chose Zettlr is:
While many Markdown editors don't offer specific support for a certain type of workflow, or offer features for scientific workflows only, Zettlr offers features that help the writing process of journalists or researchers in the arts and humanities. It's a lot more text-focused than most editors.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
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
Pro Focuses on writers
While many Markdown editors don't offer specific support for a certain type of workflow, or offer features for scientific workflows only, Zettlr offers features that help the writing process of journalists or researchers in the arts and humanities. It's a lot more text-focused than most editors.
Pro Citation support
While it supports a diverse range of syntax (chart, easy image insert, etc.) found in other editors, the great citation support made it possible to write real articles. Citation from Zotero and Mendeley can be inserted easily which is a huge plus.
Pro Almost perfect
This is the best option, still not perfect, there are some bugs like creating / editing tables and resizing images, but the PROS destroy the CONS, easy quotes, WYSIWYM , attachments tab (supports attaching and opening links to any file), table of contents, TAGs, easy hyperlink between files (same as citations), export to many formats (like Word, HTML5, PDF)...
Pro Renders math in-place through KaTex
Cons
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.
Con Obtrusive, like someone WITH CAPS LOCK ON
Too loud, too much going on, and definitely an in-your-face sort of feeling.
Con Large, slow, can't open just a single .md file
