Usually I just use whatever fonts are default on the DE I happen to be using at the time, right now that’d be GNOME so I believe its Cantarell? I don’t generally customize my normal (non-monospace) fonts because I can never find one that looks good everywhere. I like Google’s “Product Sans” font for example, but it is definitely not one you want to use everywhere. Yet oddly enough on my Pixel, I believe Product Sans is the default unless an app explicitly changes it, and it looks good everywhere there. Or maybe I’ve just never given changing the default enough time to adjust to it, who knows.
The monospace font that I use is Comic Code, it sounds silly I know (I was skeptical at first too) - but it looks really nice in both my terminal and IntelliJ. Something about the font renderer that is used by default (I can’t think of the name for some reason, FreeType maybe?) makes it look really nice and sharp. On Windows, it looks too thin, and on macOS it looks too thick - Linux is truly the “golidlocks” for this font it seems.