When comparing typora vs iA Writer, the Slant community recommends typora for most people. In the question“What is the best cross-platform note-taking app?” typora is ranked 13th while iA Writer is ranked 52nd. 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 Noise Free Writing Experience removes even the program bar
The Noise Free Writing Experience is one of the first approaches to create a first class distraction-free environment. The feature hides the Mac program bar when you start writing.
Pro A mode that brings focus to the sentence you're working on
Enabling Focus Mode will dim the whole text except the sentence you are currently writing on.
Pro Can tell how long it would take to read through what you've written
Pro Markdown support
Pro Syncs using iCloud and Dropbox
iA Writer can sync documents using iCloud or Dropbox from within the editor for use across multiple devices.
Pro Create whole document by including separate images/markdown docs
This is new and very awesome feature in iA Writer 4.0.
Pro Can export a Word document
Pro Available for all Apple devices
iA Writer is available for Mac, iPhone and iPad.
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.
Con No Linux support
