When comparing StackEdit vs Apple Notes, the Slant community recommends Apple Notes for most people. In the question“What is the best cross-platform note-taking app?” Apple Notes is ranked 18th while StackEdit is ranked 28th. The most important reason people chose Apple Notes is:
It syncs with iCloud, and surprisingly, also with Gmail and possibly other services too.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Works online and offline
StackEdit works within your browser. You need internet access to connect to the website, but once it's loaded, the site does not require an internet connection - you will be able to edit and save files locally. Additionally, you can use Fluid to turn it into a native desktop application.
Pro Supports various Markdown flavors
Supports standard Markdown and Markdown Extra.

Pro Simple workflow
It is very easy to toggle between the preview and the editing windows. The black makes it a very focused writing environment. Of course it's possible to change that if needed.

Pro Great when in full-screen
Pro No need to install additional software
StackEdit works directly from the browser, there's no need to install additional software as long as you have a web browser installed on your computer.
Pro Real-time preview
The preview shows in a collapsible pane on the right hand side.
Pro Instant publishing
StackEdit allows pushing a document directly to a list of publishing or file storage platforms or any SSH server.
Pro Multiple export options
Can export to .txt, .html and .pdf.
Pro Syncs via Dropbox and Drive
Files can be synchronized through Dropbox and Drive.
Pro Sync with other Apple devices via iCloud, other cloud/email services
It syncs with iCloud, and surprisingly, also with Gmail and possibly other services too.
Pro Built-in
It's a default system app, making it easy to find and use since it is already installed.
Pro Rich-text editing
Allows for simple text formatting and making TODO lists with checkboxes.
Pro Attachments
You can add files to notes and then filter notes by attachment types.
Pro Supports sharing
Pro It's fast, and syncing is very dependable
The app launches quickly on both Mac and iOS, it also syncs quickly (in seconds) and very dependably across different Apple devices.
Pro It remains simple to use with a gentle learning curve
Despite the significant new updates in iOS 9 and iOS 10, you can start using Notes immediately, then try/master new features with ease — definitely a gentle learning curve.
Cons
Con Saves files in browser's local storage
Local storage is limited and if the browser crashes the text can be lost.
Con Cannot be accessed while being offline
Even though the editor itself works offline, you need internet access to open the website and the editor.
Con Lacks a good integrated spell checker
Uses the built-in browser spell checker which may not be as good as spell checkers other editors have. Depending on the browser, of course.
Con Publishing to GitHub requires giving write access to repos
In order to publish documents to GitHub, StackEdit requires writing access to your repos, something which many people may not be comfortable with.
Con Cannot export to a format that can be imported again
This makes it obscure and cumbersome to back up your notes as files that could be managed by your backup system. You can export to PDF, but not in bulk; and this isn't the native format that you can easily recover with.
Apple compounds the problem by using some undocumented format for notes. You can, however, back them all up by backing up the files found in ~/Library/Containers/com.apple.Notes/Data/Library/Notes
