When comparing typora vs OmmWriter, the Slant community recommends typora for most people. In the question“What are the best distraction-free word processors?” typora is ranked 5th while OmmWriter is ranked 7th. The most important reason people chose typora is:
Typora immediately renders what's typed on the screen in Markdown format. This helps users to have a better understanding of how their document is being formatted.
Specs
Ranked in these QuestionsQuestion Ranking
Pros

Pro Live preview
Typora immediately renders what's typed on the screen in Markdown format. This helps users to have a better understanding of how their document is being formatted.

Pro Hybrid interface
The editor and preview dual-pane setup typical of desktop Markdown editors are gone; instead, a singular interface makes for a WYSIWYG experience. This streamlines the workflow and encourages direct manipulation.

Pro Support for LaTeX expressions
It supports LaTeX expressions, with an easy-to-use MaxJax panel.

Pro Syntax highlight for fenced codes
It supports GFM's code fences, with syntax highlight support for C/C++, java, etc.

Pro Custom theme support
Typora has clean yet beautiful built-in themes and allows for users to create new themes using CSS.

Pro Support for tables
It supports tables for Markdown Extra. And also provides a GUI to make it easy to insert and edit them.

Pro Inline images
It won't display image like 
, But shows the image content inside the editor.
Pro Free during beta
Pro Shows table of contents for the document
It supports an outline for the document, by showing a table of contents on the left side of the screen.
Pro Cross-platform
Currently works on Windows, Mac and Linux.
Pro Natural typing experience
Editing in Markdown, either in WYSIWYG mode or in markdown code mode, feels natural. It never gets in the way.
Pro Make charts and diagrams with Mermaid, FlowChart and Sequence
Use fenced code-blocks to render diagrams using syntax from Mermaid and FlowChart.js.
Pro Sidebar with a list of files
You can open any folder in sidebar and see a list of other markdown files.
Pro Syncs with iCloud
Pro Offers a selection of great backgrounds, audio tracks and keystroke sounds to add ambiance
OmmWriter's greatest strength lies in a great selection of pleasant visual designs (images, photographs and chromatherapy backgrounds) and immersive music that can change the look and feel of the writer allowing to create desired ambiance. The backgrounds choices are calm and unobtrusive and the ambient music options are enveloping. You can even choose to replace keyboard strokes with different kinds of sounds. These elements, together with a clean design, create a feeling of a space that's separate from all distractions found in world around you.
Pro Blanks out the any other screens if you have more than one
Pro Monospace font support
Pro Exports to a .omm, .txt and .pdf files
OmmWriter can save to plaintext files (.omm and .txt are both plaintext, only the extension is different) and PDF documents.
Pro Cross-platform
OmmWriter is available for OS X 10.5+, Windows XP - 7 and iPad iOS 3.2+.
Cons
Con No mobile (Android/iOS) apps
Con In beta
Typora is still in beta and may be prone to changes or bugs.
Con Unusable image management
Con The immediate rendering of Markdown is hard on the eyes
Having Markdown immediately render causes text to jump into formatted text, which is distracting and hard on the eyes.
Con No portable version (Windows)
You need admin rights on a managed Windows computer to install it. There currently is no portable version available.
