Using Joplin right now. I wouldn't say I'm blown away by it, but it fits some simple needs for a digital notebook:
* Markdown and LaTeX working stably out of the box. * Side-by-side view. * (Isolated) File and folder browser in the immediate UI
I originally started with it because it's Open Source and can link to other documents saved in Joplin - I don't actually use that feature though.
Other than that it's fairly sane. Just works, no real bugs so far, and you can export in a variety of different convenient formats; I've come to trust exporting as a single .jex (Joplin Export) file, but MD and HTML are supported.