Bert, this is a matter of personal opinion. I agree the books you've chosen are good but I liked Citadel more than Golden Keel. While Moon Is A Harsh Mistress was very good I would put Stranger In A Strange Land and Time Enough For Love ahead of it. I haven't read the other authors. I will have to admit that it has been years since I read any of the above books (your choices and mine). Still they all have remained lodged in the spaces between my ears while other lesser books have slipped away.

Still, you bring up a good point. Some authors do indeed only have one masterpiece in them. And some authors only have one book in them, much to the reader's sorrow.

Is there anything you'd like to offer to support your statements or your choices for the title of masterpiece?