I personally recommend
Captain Stormfield's Visit to Heaven,
The Man That Corrupted Hadleyburg and
The Tragedy of Pudd'nhead Wilson.
The central theme of
The Mysterious Stranger has become trite, although i suspect it was fresh in its time. His wife and daughter both became devotées of Mary Baker Eddy and Christian Science, and both died in horrible agony. He was enraged. He wrote
Christian Science. It's scathing condemnation of the cult was greeted with horror by the contemporary religious community, and it was withdrawn, and many copies were destroyd--many others were burned in public demonstrations by the "faithful." It was out of print for more than 75 years--although i did see it in paperback about ten years ago.
A Connecticutt Yankee in King Arthur's Court is good, but a little obscure to those unfamiliar with his life and times. Having received a letter from a popular novelist of his time, who asked him if he couldn't have written more in that book, he replied yes, but it would have taken an entire library "
. . . and a pen warmed up in Hell."
About a decade ago, Mr. Clemens' more biting critical satire was put together in a slim volume which was given that title:
A Pen Warmed Up in Hell. It is not for the faint of heart. It includes his devasting comment on the rah-rah patriotism of the Spanish War,
The War Prayer. I have linked it here, because i recommend it to all and sundry.
He has got to be the most "quotable" American who has ever lived. Mr. Clemens is to me, the quintessential, no BS American. This one expresses, to my mind, just what his character was all about:
Education: that which reveals to the wise, and conceals from the stupid, the vast limits of their knowledge.