GNU nano.

I don't know why I bothered using Vim, Neovim, Micro, mg, and JOE for so long, when nano was always there (though not necessarily OOTB), configurable with all of the features I used in the other editors, and has never broken as long as I've been using it.

The only editor I may leave it for would be Emacs, and that would be more for the extension scripts and an excuse to learn ELisp than anything else.