The character bugging me is the lowercase i - it looks like a little 1 with a dot on top if you can squint that hard, it's worse not better than DejaVu Sans which I use.

(edit: the lowercase a is also rapidly gaining my dislike, it's all smashed up and looks weird)

If you're really using DejaVu Sans, that's a proportional font, so the difference to a "mono" font will be pretty big, especially for the usually narrow letters (i, j, l...) which have to be "padded" in mono fonts to avoid looking unbalanced (and, for coding, to make them easier to distinguish). Of course, if the other letters are as geometrically clean as in this font, the "i" will look a bit out of place. But actually in DejaVu Sans _Mono_ (https://www.fontsquirrel.com/fonts/dejavu-sans-mono), the "i" looks pretty similar.

I follow - the default system level (meaning without me tweaking it) fontconfig maps "Monospace Regular" to DejaVu Sans, not DejaVu Mono - so in reality, my "non mono" font is more readable to me (we all know this is subjective) than this actual mono font. I do map Courier to DejaVU Sans Mono in my own custom config, but never actually use that font - it's more for web rendering and stuff to look nice.

Outside of terminal windows and places where Monospace Regular is used automatically, I tend to use Luxi family as my font -- it used to be shipped with RHEL in the 90s, was removed due to license problems (or so I'm to believe) in one of the Fedora Core releases. https://en.wikipedia.org/wiki/Luxi_fonts