Right now, I don't think any of us use Sass/Scss, Less, or Stylus to the point where switching back and forth isn't possible. They're all basically the same until you get into the super power user features which, none of us have embraced quite yet.
#Sass/Scss
We obviously know what Sass and Scss are. I think the css-compatible format is pretty nice option even though, ascetically, I prefer sass.
body
background-color:red;