Comparison of CSS Preprocessors SASS vs LESS vs STYLUS

Comparison of CSS Preprocessors SASS vs LESS vs STYLUS
CSS Pre-processors add power and elegance to the basic language. By extending CSS with variables, operators, interpolations, etc. they keep large stylesheets well-organized and improve maintainability. Not only they will allow the application of sound engineering principles such as redundancy reduction and reuse but they will act as an abstraction layer between the project and the browser vendors. In this article we will compare the most popular open source CSS preprocessors.
Compile Time Verification
This will ensure high quality assets.
Syntax

Sass and LESS both use the standard CSS syntax where as Stylus uses and extended syntax.

Variables

All three support variables that should reduce redundancy.

Mixins
These are equivalent to methods and functions. Stylus has the syntax the most closely resembles Javascript.
One common reason to use mixins is to abstract out the differences in browser vendors and and create vendor prefixes.