I would say that the Pentagon Papers case of 1971 - in which the government tried to block the The New York Times and The Washington Post that they obtained from a secret study of how we got involved in the war in Vietnam - that is probably the most important case.

Floyd Abrams is an American lawyer who is considered one of the preeminent First Amendment attorneys in the United States. He is known for representing major media organizations in cases involving freedom of the press, including The New York Times in the Pentagon Papers case, as well as representing individuals in cases involving freedom of speech and expression. Throughout his career, Abrams has argued numerous cases before the United States Supreme Court and has been involved in some of the most prominent First Amendment cases of the last several decades. He is currently a senior counsel at Cahill Gordon & Reindel LLP in New York.