Comparing CSS PREprocessors

CSS

Variables

Less Sass Stylus
Basic
Ability to declare variables and use them later
Default
Default variables are overwritten by regular ones, no matter when they are declared
Lazy
Variable Hoisting, variables can be declared after being used
Lookup
Use the value of a previously declared property elsewhere
Scoped
Restrict the scope of variables

source article: csspre.com/compare/