In terms of self-assessment, Smith made various pronouncements on what he considered his best work. These included the six stories in [The] Double Shadow (i.e., "The Voyage of King Euvoran," "The Maze of the Enchanter, " "The Double Shadow," "A Night in Malnéant," "The Devotee of Evil" and "The Willow Landscape") and the individual stories "The Eternal World" and "The City of the Singing Flame." He named "The Uncharted Isle" as the best "or at least favorite" of his "straight science fiction" stories. Toward the end of his life, Smith considered his "masterpiece" to be the blank verse play, "The Dead Will Cuckold You" (1951, 1956) set in Zothique, one of his last completed works. Of his Zothique story cycle taken as a whole, Smith said it was "in no wise inferior to Dunsany and Cabell." Regarding his poetry -- which he took the most seriously of all his creative work -- Smith felt (writing in 1936) that he had produced his best work in the years 1913-23.
http://alangullette.com/lit/smith/sorcerer.htm
Note: Book titles are italicized -- The Double Shadow -- whereas, individual stories or poems -- "The City of the Singing Flame" -- are placed within quotation marks.