When comparing Hack vs Google Roboto Mono, the Slant community recommends Hack for most people. In the question“What are the best programming fonts?” Hack is ranked 7th while Google Roboto Mono is ranked 26th.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Very readable
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 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 Avaliable in many GNU/Linux distro package manager
Including Debian/Ubuntu (fonts-hack), Fedora (font-hack-ttf), OpenSUSE (hack-fonts), Arch (ttf-hack) and probably many more. Much nicer than having to manually install/update
Pro Free/Open license
Pro Renders accurately on Windows on all font sizes
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 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 Looks really beautiful
Roboto Mono has a very clean and beautiful design.
Pro Clean and legible
Roboto Mono is crystal clear which makes it a good choice for reading code without your eyes getting tired.
Pro The right thickness
It's neither too thin, too fat, nor too condensed. Roboto Mono is just right.
Pro All variants available
Both bold and italics look great in Roboto Mono.
Pro Distinctive uppercase vs lowercase characters
The median line is placed relatively low. This makes reading mix-cased words (eg. hashes) easier.
Pro Readable, elegant and cute
It's very readable, elegant and cute. Almost indistinguishable with SF Mono at small point sizes. It looks great even as a display font.
Pro Makes for an excellent font for terminal
Roboto Mono looks particularly well on iterm2.
Pro Released under the lenient Apache License
Pro Powerline Patched version works well
This is the only font that works well and looks good with agnoster theme and powerline for bash/zsh.

Pro Looks great on HiDPI
Looks good at 14pt and lower, but looks great at 20pt and higher, making it an excellent font for higher resolutions
Cons
Con No ligatures in the default font
Although patched versions with ligatures do exist - see here.
Con Sometimes difficult to distinguish lowercase "i" (eye) and lowercase "l" (ell)
When using a higher resolution monitor and a smaller font size, the lowercase "i" (eye) and lowercase "l" (ell) 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" (ell).
Con Too similar to DejaVu
See this gif comparison between the two fonts.

Con Curly braces aren't very distinctive
The curly braces are too close to parentheses, which can harm readability for programming.
Con Not recognized as monospace font
Windows does not recognize the font as monospaced. Cannot be used as terminal font.
Con Sublime Text doesn't show italic version
font face "Roboto Mono" has different widths for italic characters, disabling to prevent text reflow
