The Holy Rosary. The Glorious Mysteries led by Mother Angelica to pray on Wednesdays and Sundays.

Our Lady's 15 Promises for Praying the Rosary
Besides the Indulgences attached to the Rosary, Our Lady revealed to St. Dominic and Blessed Alan de la Roche additional benefits for those who devoutly pray the Rosary. Our Lady's promise is shown in darker blue text. Additional explanation on and doctrinal connections to each promise is shown following in the smaller normal text font and color. Note that the Rosary is the prayer (non-Liturgical) with the most published Magisterial / Papal documents expounding on its excellence. Vatican II's summary on Our Lady is contained in Lumen Gentium chapter VIII.
Signal Graces are those special and unique Graces to help sanctify us in our state in life. See the remaining promises for an explanation for which these will consist. St. Louis de Montfort states emphatically that the best and fastest way to union with Our Lord is via Our Lady [True Devotion to Mary, chapter four].
Reminder: these promises mean that, by faithfully and devoutly praying the Rosary, Our Lady will obtain for us the necessary Graces to obtain said promises. It is still up to each individual soul to respond to those Graces in order to obtain salvation.