When comparing Hack vs Operator, the Slant community recommends Hack for most people. In the question“What are the best programming fonts?” Hack is ranked 8th while Operator is ranked 49th.
Ranked in these QuestionsQuestion Ranking
Pro Very readable
Pro Fixes many readability issues in Vera/DejaVu
The tilde symbol ('~'), comma (',') and semicolon (';') glyphs have been modified to be more readable at small sizes and/or on non-HD displays. In addition, the underscore symbol ('_') has been slightly lifted for alignment with surrounding characters.
Pro Based on the tried and tested Bitstream Vera Sans Mono
The fonts are in the Vera Sans Mono lineage with a significant expansion of the character set (which includes Cyrillic and modern Greek character sets), new glyph shapes and modifications of the original glyph shapes, as well as improvements in metrics and hinting/TT instructions to make it more legible at small text sizes used for source code.
The changelog is available here.
Pro Libre webfonts are available in svg, eot, ttf, woff, and woff2 formats
Hack is free for unlimited commercial and non-commercial use. The webfonts are hinted (TrueType instruction set) to optimize display on the screen and are built into all commonly used web font formats with each new release. They include the complete release character set and smaller (filesize) basic Latin subset releases. They are available in the build directory of the repository.
Pro Powerline glyph patch is included
The regular set is patched with Powerline glyphs by default. There is no need to patch the font to use it in Powerline environments.
Pro Source code is released in UFO format
UFO source format is widely supported by all modern font editors if you would like to modify the typeface.
Pro Has a script version
Operator can be used to mix the same font for syntax formatting.
Pro Super readable
Long strings can be read in Operator exceedingly easily. The font just flows nicely, with all the benefits of clarity that provides.
Pro Horizontal width not as wide as other fixed width fonts
You can legibly read everything and get more characters per line.
Pro Adorable italics
Con Too similar to DejaVu
See this gif comparison between the two fonts: https://gfycat.com/SomberUnitedGermanshepherd
Con Sometimes difficult to distinguish lowercase "i" and lowercase "l"
When using a higher resolution monitor and a smaller font size, the lowercase "i" and lowercase "l" are very difficult to distinguish. The space between the dot and the remainder of the letter seems to somehow disappear, thereby making it look like a solid line, similar to the lowercase "l".
Con Relatively expensive
At $179, this font is on the more expensive side.