Major Barbara
A Salvation Army officer discovers her charity is funded by her arms-dealer father's profits, and has to decide which one of them is the real hypocrite. Shaw was the only person to win both a Nobel Prize and an Oscar, and this play shows why: he could make an argument about capitalism feel like a boxing match. The dialogue moves at the speed of thought.
Shaw's characters are positions with hats. Undershaft wins the argument because Shaw rigged it, Barbara's conversion in the last act happens at the speed of a syllogism rather than a soul, and the munitions-factory finale turns into a seminar. As debate it's thrilling; as drama, you keep waiting for someone to behave like a person instead of a paragraph.
The case for it and the rest of the canon open with Pro.
