The answer to your question really depends upon your definition of 'popular'. Quotations from Chairman Mao might have had plenty of copies printed but I'm not sure that all those people who received copies would regard it as 'popular' :-)
Most lists have the Holy Bible in 1st place (in terms of copies published).
2nd place goes to Chairman Mao.
In 3rd place is the leading work of fiction, which is way ahead of anything by Shakespeare. It's 'Don Quijote de la Mancha' by Miguel de Cervantes.
Chris