Default

.foo {
  color: red;
  display: block;
}

Banner

.foo {
  color: red;
  display: block;
}

Saver

.foo {
  color: red;
  display: block;
}

Aligned

.foo {
  color: red;
  display: block;
}

Pico

.foo {
  color: red;
  display: block;
}

Extra

.foo {
  color: red;
  display: block;
}

GNU

.foo {
  color: red;
  display: block;
}

HMANN

.foo {
  color: red;
  display: block;
}

Personally, I feel that the default style is by far the most readable, followed closely by the GNU style. My primary issue with styles such as saver or pico is that you cannot move entire lines up and down due to the first and/or last declaration sharing a line with the selector or bracket.

Note: I couldn't actually find documentation to verify some of these naming conventions. If anyone knows a source or possibly a different name for a style, reach out on Twitter: @benjamincharity