When comparing Polynote vs Quiver, the Slant community recommends Polynote for most people. In the question“What is the best cross-platform note-taking app?” Polynote is ranked 59th while Quiver is ranked 65th. The most important reason people chose Polynote is:
Multiple users can edit a note simultaneously, in real time.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Real-time collaborative
Multiple users can edit a note simultaneously, in real time.
Pro Minimal interface
The application is simple and fast. Can create, share and organize notes and notebooks on the same page.
Pro Has more features than just a simple Markdown editor
Quiver is a notebook and note-taking app akin to Evernote which happens to also be able to edit Markdown files. As such, it has a lot of useful features such as: image support, file attachments, web content support and more.
Pro Supports code highlighting
Has syntax highlighting for more than 120 programming languages.
Pro Notes can be linked to each-other
Quiver notes have unique links that can be copied and pasted into other notes to gain quick access between them.
Pro Live preview
Quiver has live preview for both Markdown and LaTeX. This helps users to better understand the way they are formatting their files.
Pro Cloud syncing
Dropbox, iCloud Drive, Google Drive, or any other file-based cloud services.

Pro Supports vi keybindings
For people used to vi keybindings, Quiver can be set up to work with them.
Pro Combination of different types of writing in one note
The most outstanding thing for me. Use HTML line breaks while writing MD text.
Also, unlike most hybrid editors like Bear, it supports instant image sizing and respective preview.
Cons

Con No free tier
Plynote has a 15-day free trial after which it requires a 20$/user/year subscription.
Con You can't edit specific files, they must be in your notebook
Con No iOS apps for editing, only a viewer available
I'd LOVE to edit and create quiver notes on my iPad!
Con The line in focus shows a border around it which is distracting
The line in focus in the editor shows a rounded rectangular border around it, which is unappealing and distracting.
Con Much more than a simple Markdown editor
Since it's more like a note-taking app (and a note-taking app built for developers) than a Markdown editor, it may be a little excessive to use it only for its Markdown editing features.
