IMHO Notable is better than Boostnote for the following main reasons:
- It supports attachments, sooner or later you are going to need to add an image or pdf to a note. The only way of doing that with Boostnote is linking to the absolute-path of that file, which is not portable nor ergonomic.
- Notes are stored as plain Markdown files, you can also edit them with your editor of choice. For instance I can use the fancy Markdown plugins I have in my editor easily.
- Multi-note editing is fully supported, from starring/tagging multiple notes at once to performing a regex search & replace across your notes. Boostnote has very limited multi-editing capabilities, and while you could technically perform a search & replace with Boostnote's notes too they are stored in .cson, which complicates things.
- Boostnote is too ugly for me. This may not matter for you but it matters for me.
- Boostnote can't import Evernote's .enex files. Notable can and it preserves both tags and attachments.
- Boostnote isn't keyboard friendly. I don't like the dual pane editor, but if I disable it there's no (documented?) shortcut for switching between editing and preview mode.