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.
“I am fully persuaded that thousands of our fellow-men might profit equally by a similar course to mine; but, constitutions not being all alike, a different course of treatment may be advisable for the removal of so tormenting an affliction.”