Difference between uncss and purifycss

I'm already using uncss with grunt, but stumbled upon purifycss.

I can't seem to find comparisons anywhere.

Can anyone tell me the difference between the two to help me choose the right one?

How does purge CSS work?

PurgeCSS works by analyzing your content files and, based off what selectors it finds, removes rules from your CSS files before including them in the final bundle. This makes PurgeCSS a build-time optimization.

UnCSS removes unused CSS from your stylesheets.

PurifyCSS does not modify the original CSS files.

I use PurifyCSS and I full recommend.

I hope that simplify the things for you, everyone has a way to do the things. If I were you I would test both and see which one is more helpful for you.

EDIT: PurifyCSS takes also care about JS-Files which could add CSS classes and IDs.