When comparing StackEdit vs Notion, the Slant community recommends Notion for most people. In the question“What is the best cross-platform note-taking app?” Notion is ranked 7th while StackEdit is ranked 28th. The most important reason people chose Notion is:
Even the right-click menus on the web are the same as the app.
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 Full-featured on desktop, mobile and web
Even the right-click menus on the web are the same as the app.
Pro Unlike anything else
One of the most complete applications one can use to build a personal dashboard (or professional) and migrate all other services to it. No more calendar, task, notes, financials, lists, writing and wiki apps, just Notion.
Pro Pages within pages within pages, to infinity
You can have a ridiculous amount of information within a single note. Look at how it works, you'll be surprised!
Pro Flexible contents storage and organization
You can upload files and embed online stuff in any hierarchical structure using pages, toggle lists, etc.
Pro Highly visual, with icons next to every new page and so on
This feature makes it very easy to find certain notes and such. And great for visual people as well. You could also add images as icons instead, if you like.
Pro Blocks offer incredible flexibility
The basic unit of organization in Notion is the block, which can be a chunk of text, an image, a bullet point, or even a link to another page. Each page consists of these blocks, which can be easily reorganized, moved to other pages, converted into other content types, or generally manipulated in many useful ways. Because of blocks, restructuring information in Notion is way easier than in any other wiki or notebook app.
Pro Does a great job with both notes and to-dos
To-dos in Notion aren't just dot point lists. You can drag and drop them into columns just like Trello (Kanban style), you can have sub-tasks, and you can easily mark things off as completed so they are no longer in your way. Notes are also powerful, with proper formatting and ways to manage and search for them, which makes it a great Evernote alternative.
Pro Cross platform
Works with Android, iOS, Windows, & Mac OSX.
Pro Awesome for wikis
You can easily start writing a bunch of web pages, share it with co-workers and choose whether to publicize or keep your contents private. It's also easy to hyperlink pages.
Pro Amazing view flexibility
You can create different views for a page's content and easily toggle between kanban, table, etc. (As long as the content is able to allow different views.)
Pro Quick and effective search
Just type in a word and you'll have results in no time at all.
Pro Attach files in tables
You can attach files in table cells, which is a feature missing in most spreadsheet-like applications.
Pro Great spreadsheet functionality
You can use calculation/formula, links, attachment, inter-referencing of data from other pages or tables, embed documents and images in the table cells.
Pro Renders Markdown Syntax
Add code blocks, Headers, bullet point, numbered lists, or To-Do boxes by typing using Markdown Syntax (instead of klunkily moving the mouse to formatting boxes)
Pro Less headaches when editing pages
Lets you restore your page to a past edit. Also works with sub-pages and databases. Though it is worth mentioning that it's a paid feature.
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 Not very fast using native apps
Can take time if you're switching between lots of pages often as it needs to load the data each time
Con Not always very intuitive
Column filters are not that intuitive to apply.

Con No true backup
True backup can only exist if it's automated and easily recoverable. Else, it's just an outdated copy or useless scrambled data.
Con Designed with teams in mind, and less formatting than Evernote
Evernote may be more individual-oriented and has more formatting and such options available, but whether that affects you is down to personal preference. Try both and see which you prefer.

Con Not yet a new protocol, as it could be! (or could it?)
Think of scuttlebutt or email. the best Evernote alternative would be a "web 3.0" of sorts. Something that would be just a simple file added to a computer and automatically replicated to other computers along with a website and any company could easily pick up the concept and make their own hosting, including some awesome google drive/host of sorts.
