Won out in what sense? Last I checked there are no formal figures about usage for either. Bootstrap's phenomenal popularity ought to make it a kingmaker for the preprocessor it uses, I suspect.
Well, the CSS preprocessor ecosystem is a clusterfuck (pardon my french).
Since the differences are so marginal I wish projects would pick their preprocessor by the number of available implementations (in popular languages) rather than the latest fashion.
Less and stylus only have javascript impls and should be avoided for that reason alone. The same applies for most other niche processors.
Like it or not, SASS appears to be the only one with a C library that enables a wide range of language bindings.
Recently I was investigating using LESS on windows. I didn't want to do it at run-time a la DotLess, but at build-time. I wasn't able to install node.js so i had to scout around for other options...
It leverages the fact that windows has long supported running JavaScript (OK technically "JScript") outside of the browser, without node, to create a command line utility from the less.js implementation. Works perfectly :)
