I am of the opinion that there isn’t really a good editor for Android, but Joplin is probably as good as we’re getting. (I love iA Writer, but it’s not as good as it could be on Android.)

I think the sync server is Joplin’s secret weapon on this front. I tried using Syncthing for managing my docs for a while, but I think having a dedicated sync server helps on mobile. I found using alternative sync methods was too wonky on a mobile device.