My article Interpreting and Drafting Efforts Provisions: From Unreason to Reason is in the summer 2019 issue of the journal The Business Lawyer, published by the Section of Business Law of the American Bar Association. (PDF here.)
The article refers to instances of the phrases best efforts and reasonable efforts the Corpus of Contemporary American English, or COCA. Go here for an Excel spreadsheet of all instances of best efforts; go here for a random sample of 100 of those instances; and go here for all instances of reasonable efforts.
The article says that no instances of best efforts in the random sample were from a legal context. The only one that came close was a reference to a best-efforts securities offering. I decided to consider that as pertaining to business, not law.