I really like Atom. It has recently been updated to work with current obsidian versions and now works beautifully with canvas boards too.
Typomagical. I love serif fonts.
Minimal theme, without a doubt. It increases customization of the editor immensely, I can hide whatever I don't need, focus mode is neat, and generally it feels not too far from vanilla obsidian experience
I loved Gruvbox from the moment I first tried it, but couldn't live without Things' tasks status, so... I'm using Things as active theme, but I've added Gruvbox's entire CSS as a snippet. Beautiful beast.
Another vote for Gruvbox. I use it on everything I can. Nice and easy on the eyes.
I really like Atom. It has recently been updated to work with current obsidian versions and now works beautifully with canvas boards too.