I refuse to use any preprocessors.
I’ve been creating sites since before CSS was in existence, so I’ve seen a lot of new trends, frameworks and the like come and go in that time. Not all of them have been bad, but a lot of them, mainly frameworks, have only made HTML or CSS even more complicated.
Let me tell you a secret: CSS is NOT a programming language. The beauty of CSS is that it’s so easy for almost any to pick up quickly and read (though it’s very difficult to actually use it properly for the big stuff). Adding a preprocessor on top just needlessly complicates and adds yet another piece of bloat to an already over bloated workflow.