cream of the crop vs greatest thing since sliced bread

cream of the crop

noun
  • The best or most desirable among some selection. 

greatest thing since sliced bread

noun
  • Something amazing, outstanding or praiseworthy, especially a relatively recent invention likely to improve people's lives. 

How often have the words cream of the crop and greatest thing since sliced bread occurred in a corpus of books? (source: Google Ngram Viewer )