J.M.J. Choosing a good book about Mary, given the large number of them, is more difficult than trying to decide what kind of chocolate to eat.
There are innumerable fine books about Our Lady.
Here is a good one for Advent:
Mystery of Mary
by the Reverend Paul Haffner, S.T.D.
(Chicago: Hillenbrand Books, 2007)
paperback, 304 pages
Do you have a favorite volume about Mary?