Polar is a document management platform which support rich annotations around your documents including reading progress.
Comments, flashcards, etc.
Rich text / HTML was a big requirement.
I also wanted advanced features like mathematics / latex and pasting of HTML from your existing tools.
I actually ended up using Summernote:
which was interesting as it's a bit older and not actively developed as much as the alternatives.
I think the big deciding factor for me was that it handled rich pasting better than all other platforms. I can copy from my editor (IntelliJ) and paste into it and the format is preserved perfectly.
With other systems this didn't work.
The BIG downside though is the size. It's huge and requires jquery (which is also huge).
I think what I'm going to do is bifurcate my app into two parts. The basic app is setup to load quickly and then the resources for the annotation come 1-2 seconds later.
Most people read for a bit before they're ready to start working with the document.
This give me time to download things in the background.
I just tested the above scenario (copy from my editor) and pasted into prosemirror and it couldn't handle it. In fact nothing happened.
I wish there was a CLEARLY obvious winner here but we're still all over the map in terms of functionality and feature set.