When comparing CSSO vs cssnano, the Slant community recommends CSSO for most people. In the question“What are the best CSS minifiers?” CSSO is ranked 2nd while cssnano is ranked 5th.
Ranked in these QuestionsQuestion Ranking
Pro Great compression
CSSO is becoming one of the fastest structural CSS optimizers available.
Pro Actively developed
Pro Can use usage data for better compression
You can include a file of usage data for better compression. Read more here.
Add needed prefixes and remove unnecessary based on its browsers option and can I use data
Pro Whitespace & final semicolon removal
Trims whitespace inside and around rules, selectors & declarations, plus removes the final semicolon inside every selector.
Pro Comment removal
postcss-discard-comments removes comments in and around rules, selectors & declarations. Note that any special comments marked with ! are kept by default.