It's very interesting, however, that no one minifier is a consistent winner in these test cases, and that running CSS through multiple minifiers is actually, potentially, not all that crazy. (The very debatable real value in doing that notwithstanding.)
Have you seen my post on the Remynifier, where I do exactly that?
I've mentioned it before, but it's really not a great idea to use multiple minifiers. Minifier bugs can get nasty, and using multiple minifiers exponentially increases the likelihood that you'll encounter some weird or broken behavior. Make sure to test thoroughly.
It didn't possibly create bugs by rewriting to new units (especially poorly supported units like q) and had the best results overall.
I'd like it to be a wee bit more aggressive on the rounding but other than that it seemed a clear winner.