When comparing Gitit vs iA Writer, the Slant community recommends Gitit for most people. In the question“What is the best cross-platform note-taking app?” Gitit is ranked 36th while iA Writer is ranked 50th. The most important reason people chose Gitit is:
Giti has a multitude of formats that it allows to be exported, including LaTeX, ConTeXt, DocBook, RTF, OpenOffice ODT, and MediaWiki markup.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Lots of export formats
Giti has a multitude of formats that it allows to be exported, including LaTeX, ConTeXt, DocBook, RTF, OpenOffice ODT, and MediaWiki markup.
Pro Supports markdown
Getit supports markdown, a plain text formatting syntax that is designed so that it can be read by HTML.
Pro Free and open source software (FOSS)
Licensed under GPLv2 so you can download source code and customize to meet your needs, provided that you know or are willing to learn Haskell.

Pro Can be used collaboratively by multiple people

Pro Renders math
Using MathJax.
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 Requires Haskell
On some Linux platforms a binary package for Haskell may not be included in the standard repositories. So, it will be necessary to compile Haskell from source code or find a non-standard package repository, which may seem like a hassle if you don't use Haskell for anything else.
Con No Linux support
