Github pages and auto updating demos ftw
Despite their marketing-y support charts, I don't think they are quite as robust as the Sass versions.
I've been led to understand in the past that the language of LESS itself doesn't make it possible to build as robust of libraries on top of it. In both cases, the onus is on you to keep the preprocessor software itself up to date as well as these libraries. For instance, Compass updates will just come automatically in Code Kit, or you use a Gem which is easy to update, while LESS mixins you'll have to manually update a file yourself.
For instance, LESS will assume the first unit you use is what you want out, ignoring further units.
In Sass, you get a clear error: Incompatible units: 'em' and 'px'.
I know that the Sass website is undergoing a major overhaul and lots of awesome people are working on it. Winner: LESS Say you declare a class which has a bit of styling.
Then you want another class which you want to do just about the same thing, only a few additional things. It rewrites selectors, which is way more efficient.
In LESS, every single class is also a mixin, programmatically muddies the waters, but is easier to understand at first. You can see some examples when we upgrade to it on Code Pen.
It's a bit funky in that it doesn't extend selectors nested in the original class unless you use an additional keyword.
That is overly simplified, but you likely get the idea. LESS can also do self-referencing recursion where a mixin can call itself with an updated value creating a loop.
if/then/else statements, for loops, while loops, and each loops. While guarded mixins are a pretty cool, natural concept, language robustness goes to Sass.
This language robustness is what makes Compass possible. It's so robust, that you can pass just about whatever you want to that thing that it will output what you need.
Maybe you should, but you don't have to, so it's not a factor here.
The fact that Sass is in Ruby and LESS is in Java Script is of little consequence to most potential users.Winner: Narrowly Sass LESS has an ability to do "guarded mixins." These are mixins that only take affect a certain condition is true.