Answer by taking a quote from the following article:

Francis Jean Marcel Poulenc (French: [fRasis Za maRsel pulek]; 7 January 1899 - 30 January 1963) was a French composer and pianist. His compositions include melodies, solo piano works, chamber music, choral pieces, operas, ballets, and orchestral concert music. Among the best-known are the piano suite Trois mouvements perpetuels (1919), the ballet Les biches (1923), the Concert champetre (1928) for harpsichord and orchestra, the Organ Concerto (1938), the opera Dialogues des Carmelites (1957), and the Gloria (1959) for soprano, choir and orchestra.

Poulenc, a highly accomplished pianist, usually composed at the piano and wrote many pieces for the instrument throughout his career. In Henri Hell's view, Poulenc's piano writing can be divided into the percussive and the gentler style reminiscent of the harpsichord. Hell considers that the finest of Poulenc's music for piano is in the accompaniments to the songs, a view shared by Poulenc himself. The vast majority of the piano works are, in the view of the writer Keith W Daniel, "what might be called 'miniatures'". Looking back at his piano music in the 1950s, the composer viewed it critically: "I tolerate the Mouvements perpetuels, my old Suite en ut [in C], and the Trois pieces. I like very much my two collections of Improvisations, an Intermezzo in A flat, and certain Nocturnes. I condemn Napoli and the Soirees de Nazelles without reprieve."  Of the pieces cited with approval by Poulenc, the fifteen Improvisations were composed at intervals between 1932 and 1959. All are brief: the longest lasts a little more than three minutes. They vary from swift and balletic to tender lyricism, old-fashioned march, perpetuum mobile, waltz and a poignant musical portrait of the singer Edith Piaf. Poulenc's favoured Intermezzo was the last of three. Numbers one and two were composed in August 1934; the A flat followed in March 1943. The commentators Marina and Victor Ledin describe the work as "the embodiment of the word 'charming'. The music seems simply to roll off the pages, each sound following another in such an honest and natural way, with eloquence and unmistakable Frenchness." The eight nocturnes were composed across nearly a decade (1929-38). Whether or not Poulenc originally conceived them as an integral set, he gave the eighth the title "To serve as Coda for the Cycle" (Pour servir de Coda au Cycle). Although they share their generic title with the nocturnes of Field, Chopin and Faure, Poulenc's do not resemble those of the earlier composers, being "night-scenes and sound-images of public and private events" rather than romantic tone poems.  The pieces Poulenc found merely tolerable were all early works: Trois mouvements perpetuels dates from 1919, the Suite in C from 1920 and the Trois pieces from 1928. All consist of short sections, the longest being the "Hymne", the second of the three 1928 pieces, which lasts about four minutes. Of the two works their composer singled out for censure, Napoli (1925) is a three-movement portrait of Italy, and Les Soirees de Nazelles is described by the composer Geoffrey Bush as "the French equivalent of Elgar's Enigma Variations" - miniature character sketches of his friends. Despite Poulenc's scorn for the work, Bush judges it ingenious and witty. Among the piano music not mentioned, favourably or harshly, by Poulenc, the best known pieces include the two Novelettes (1927-28), the set of six miniatures for children, Villageoises (1933), a piano version of the seven-movement Suite francaise (1935), and L'embarquement pour Cythere for two pianos (1953).

What did he prefer other than the 1950's music?
Of the pieces cited with approval by Poulenc, the fifteen Improvisations were composed at intervals between 1932 and 1959.