When comparing 6x13 fixed vs Google Roboto Mono, the Slant community recommends Google Roboto Mono for most people. In the question“What are the best programming fonts?” Google Roboto Mono is ranked 26th while 6x13 fixed is ranked 37th. The most important reason people chose Google Roboto Mono is:
Roboto Mono has a very clean and beautiful design.
Specs
Ranked in these QuestionsQuestion Ranking
Pros

Pro Well designed
6x13 fixed is the apex of bitmap fonts. It has a nice, defined character set and great proportions for quantity of text onscreen, making for excellent readability. It is aesthetically pleasing for a bitmap font and has been deservedly termed 'classic'.
Pro Legible at small sizes
At a small text size, each character has a limited resolution. A character size of 6x13 pixels means only 78 pixels per character. Modern fonts are designed to be scalable and are less legible at these small sizes. Using bitmap fonts increases legibility by eliminating scaling and sub-pixel aliasing artifacts. Some scalable fonts include "ppems" embedded bitmaps for this reason.
Pro Available on every X server
6x13 is the classic fixed monospace bitmap font that is expected to be available on every X server. It is part of the misc-fixed family. These fonts were handcrafted for readability in a terminal.
Pro Widely available
It is distributed alongside the X Window System.
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 Doesn't have a slashed zero
The absence of non-slashed zeroes makes it harder to distinguish "0" from the letter "O".
Con Extremely small on high-DPI screens
While it is crafted for a screen where the pixels are visible, bitmap fonts do not work well on high-DPI screens as they do not scale too well.

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
