Linux

i want serifs. I use Go Mono for monospaced text. i've yet to find a good proportional slab serif font to match though.

I love Cartograph CF for the terminal and code editor. I like the handwriting-style italic variant, and it has programming ligatures. And of course I like the way the font looks.

There is an open-source font, Victor Mono, that also has a handwriting-style italic variant and programming ligatures. Otherwise its style is quite different.

Iosevka

I know that this will anger some people, but I just use the defaults and I don't get why there are so many fonts, since they don't seem that much different to me.

Lato, League Spartan, League Gothic are my three most used fonts by a wide margin. Lato and its variety of weights for most things, League when I am doing design work and need a cleaner title or header.

Lately ive been weirdly taken with TT2020 Style G, which is an odd name for a no-name font that replicates an old imperfect typewriter. For whatever reason, switching my writing software to that (Manuscript) suddenly fired up my writing flow.

Fira Code and Caskaydia Cove Nerd Font for monospace. For other uses, I'm usually good with whatever the system ships with.

Fira Sans / FiraGO by Mozilla, and the new SUSE font by SUSE.

Ubuntu

Whatever the default font is

Poppins, RobotoMono, Comfortaa and OpenDyslexic

Noto Sans for sans-serif text (and the OS)
It's legible, standard-looking and support about every writing system in the world. You can install it on Debian using # apt install fonts-noto, some others like -cjk and -extra help with the "supports about every writing system in the world"-aspect.

Merriweather for the serif font fallback for the browser, as well as TTRPG campaign printouts
It's very legible, and looks quite sexy for a serif font. There's no package for it currently (although AUR and Nix users might have better luck), it has to be downloaded from Google Fonts

JetBrains Mono for the terminal TUI's
It looks a bit playful, like lego-letters, is legible and supports about every writing system in the world. # apt install fonts-jetbrains-mono.

Although I use...

Verdana for source code
It differentiates every character well and leaves enough space to easily recognise special characters such as brackets. And I don't believe monospace fonts are more legible. It's included in ttf-mscorefonts-installer but the font is not open-source.

0xProto

I mostly use an android, and the default font is Ideal Sans Light. On my system, Arial Nova, Courier Prime, Helvetica Neue, Ideal Sans Book and a few others are regulars.

Every once in a while I get this itch which ends up in getting a new favourite font.

Pusab (I'm a gd player)

Inter everywhere

SegoeUI, it’s damn good and well made

VictorMono, has a cool cursive, mono spaced font.

Ubuntu Mono for terminal, code, and data, Open Sans for the rest

I switched to Commit Mono for Terminal not too long ago but I really like it. Otherwise I use Cantarell but only because it is default and I never felt the need to change it.

I don’t have a reason to move away from the Fedora defaults except for monospaced fonts.

Terminal wise, terminus is my default. It’s so clean, and it looks good without anti-aliasing.

Roboto Mono is my current preference for monospaced fonts.

Adobe Source Code Pro and JetBrains Mono are good alternatives as well.

@SolarPunker I use Exo2 as desktop font and FantasqueSansMono in terminal.

Verdana, Tahoma and Source code pro is good for eyes

I don't have a favorite system font, am I meant to? I did try to play with fonts at one point but the process of finding fonts and then figuring out how to install them was a bit much.