For me, distinguish similar letters such as 0, O, I, l, 1. Then I want ligature because I like them, then emojis should align vertically to the grid, high resolution for small font sizes, size difference between tall and not-tall characters, and it shouldn't have narrow characters.

Last time when I was changing up the font I went to https://www.nerdfonts.com/font-downloads and tried out a couple until I found one that I liked. I'm really picky about the symbol shapes, I most often just bail on a font because the @, % or & is ugly I might also bail if ` vs ' is not distinct enough.

Some fonts have absolutely wild italics that are almost cursive which is a hard pass. Even though I only see it once every week maybe I'm just not up for it.