I use Emacs as my daily driver, but everyone needs a quick editor for config files and the like. I started using GNU Nano for that purpose a year or so ago, but until then I was using ed. That would make it the longest-running program I've ever used: 1976 to 2022.
I wish Vim, when started in Ex mode, wouldn't set current cursor line to lowest regardless of whether the cursor is already on it. It wastes screen, making backscroll unusable. I researched ways to configure Vim not to do that and didn't find any one that works well together with Vim's terminal support. This is the only obstacle to using Vim like ed.