I am not an expert on the subject. But I thought it's worth a try. If one looks at it chronologically, some of the oldest literature has been probably most influential. I am talking of literature in the form of Mahabharata, Ramayana, Gita, Testaments, Bible, Koran etc. These have shaped human behavior to an extent ranging from religious wars to modern day debates related to abortion, stem cell research etc. Greek literature (Homer etc.) and Indian folk tales (Jataka, Panchatantra etc.) were good reads but they didn't have any major impact on society.
And the trend continues till 19th century: Dante, Cervantes, Voltaire, John Milton, Alexandar Dumas or even Shakespeare wrote stuff that didn't really bring about major social change per se. They could have of course influenced the point of views of a good number of people. The 19th and 20th century were then clearly the ages of the novel. While 19th century giants like Victor Hugo or Charles Dickens told moralistic tales; 20th century was much more diverse with stuff ranging from G B Shaw to Sartre to Garcia Marquez.
And the last 50 years has seen an exclusive focus on the non-conformist, the outsider, the imperfect, and the morally corrupt as in the stuff from Coetzee, Salinger, Michel HouelleBecq or William Golding. Satire too regained popularity long after Voltaire and Gogol through the writings of George Orwell, Joseph Heller etc. Therefore given their very nature, late 20th century literature was not suitable to bring about any social impact on a larger scale. However, I find it surprising that apart from the ancient religious literature, the only two works that can claim to have brought about massive social change relate to the 19th and 20th Century. The first is surely Harriet Beecher Stowe's "Uncle Tom's Cabin" which can surely claim to have fermented public opinion against slavery. The second is Jack Kerouac's "On the Road" which led to the Beat Generation, then to the Hippy Generation, finally culminating in the events of 1968.