Sass vs Stylus vs LESS

less.less

.border-radius (@radius) {
  -webkit-border-radius: @radius;
  -o-border-radius: @radius;
  -moz-border-radius: @radius;
  -ms-border-radius: @radius;
  border-radius: @radius;
}

.user-list {
  // need to use special `.` syntax
  .border-radius(10px);
}

sass.sass

@mixin border-radius($radius)
  -webkit-border-radius: $radius
  -o-border-radius: $radius
  -moz-border-radius: $radius
  -ms-border-radius: $radius
  border-radius: $radius

.user-list
  // need to use special `@` syntax
  @include border-radius(10px)

stylus.styl

// This and all CSS3 funcs are included in `nib` stylus plugin.
border-radius()
  -webkit-border-radius: arguments
  -o-border-radius: arguments
  -moz-border-radius: arguments
  -ms-border-radius: arguments
  border-radius: arguments

.user-list
  border-radius: 10px


// or

.user-list {
  border-radius: 10px;
}

@Shirasho - Stylus seems to already be perfect - so, whether you buy it or not - you'll just have to try writing a project in Stylus - and then the same project in SCSS - and you will never use SCSS again. Unless you really like writing @import hundreds of times...