I was trying out the latest editor changes, when I noticed the new default script editor font, Mononoki (the screenshot was taken on Windows):

(Note: click on the images to display them in a new tab, at 1:1 size)
It looks less readable to me, compared to the previous script editor font (Source Code Pro). I've found Hack to be a very nice programming font, so I may be biased, but I feel like it's still important to start a discussion on this – readability of the default fonts used in the editor is essential to a good user experience.
@djrm sent me this screenshot of the Mononoki font on Linux, it looks better, but it's still less readable than most of the fixed-width fonts I'm used to:

He tried out the Hack font, and it looks much more readable. On this screenshot, it's a bit large, but its size could be lowered a bit and it still could be very readable:

(The license of Hack is a custom one, it's similar to the SIL OFL, but it still is DFSG-compatible so it should be good.)
Feel free to voice your opinion below :)
I'm also familiar with Fira Mono (which Fira Code is based on, but ligatures are very weird..)
https://fonts.google.com/specimen/Fira+Mono
Can you generate a screenshot for Fira Mono?
Related: #11253 #11309
Edit: Quoting myself from above thread:
Mononoki's capital O looks a bit too thin for me. Other than that they're both okay.
I agree, I dont liked the new font too, less readable in my opinion. I usually use dejavu but hack maybe it's good. I need to test.
Personally i'm very biased towards Deja-Vu Sans Mono. It's very clear and pleasant on the eyes.

The licence says Deja-vu is public domain right in the first sentence. So i'm sure that's compatible.
Comparasion of HackRegular and DejaVuSansMono inside godot with 14px:
Hack:

DejaVu Sans Mono:

I prefer DejaVu, Hack IMO doesn't works very well in small sizes, number 0 is very strange in Hack. Nevertheless, the two are very similar.
Screenshots taken on Linux.
Complementing:
Monoki:

DejaVuSansMono:

HackRegular:

DejaVu Sans Mono looks good as well (and pretty close to Hack, in fact, it seems to render better in Godot than Hack, which I haven't tried in Godot).
You guys have to admit that symbols in mononoki are great, perfectly identifiable, like * % -, also the 0 (zero)
DejaVuSansMono looks better to me.
I think I find a bug in Godot, when I use DejaVu and Hack with 13px and 14px they has the same size, this affects how DejaVu render the symbol minus "-". Normally dejavu is well aligned.
Dejavu 13px size (with minus aligned with equal):

DejaVu 14px size (desaligned and with same size of 13px):

This not occurs in other programs/editors.
Edit:
Font rendering is very annoying, each program renders the same fonts in different ways.
Edit2:
I reupload screenschot of 13px font because I select the wrong image.
DejaVuSansMono is my vote. Hack is a very close second. I like that Hack looks a bit more vibrant. Monoki is a nice looking font, but as far as code goes makes it much less readable (IE the look of the font seems to become more important than the code). So, while it looks nice, my vote is no for Mononoki.
If DejavuSansMono would look like it does in Arjan219's screenshot, my vote is a definite no, as it's very overbearing (I'm guessing he's using bold?). As long as it looks like it does in guilhermefelipecgs's screenshots above, my vote is yes to DejavuSansMono!
what about noto mono, it goes well with godot, since it uses noto sans

+1 for noto mono. It matches noto sans.
Would be great to have choice. I personnaly like Inconsolata: https://fonts.google.com/specimen/Inconsolata
what about noto mono, it goes well with godot, since it uses noto sans
Noto Mono also is a good choice, but it currently lacks bold and italic variants, which Hack has (Godot currently can't make use of these variants, but if support for font variants in the script editor is added, then this would become a problem).
@hickop you will be able to choose the font you like best, but we are discussing the default godot font.
any agreeement so far? :)
Apparently Hack wins.
I think we can close this discussion, right?
Hack is the new font now.
I guess this can be closed then :)
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Personally i'm very biased towards Deja-Vu Sans Mono. It's very clear and pleasant on the eyes.
The licence says Deja-vu is public domain right in the first sentence. So i'm sure that's compatible.