Final answer:
The Council of Trent had the most impact in the Catholic reform.
Step-by-step explanation:
The Catholic reform that had the most impact was the Council of Trent. The Council of Trent was held from 1545 to 1563 and addressed the challenges posed by Martin Luther and the Protestant Reformation. During the Council, the Catholic Church affirmed that good works and faith were required for salvation, affirmed the doctrine of transubstantiation, and implemented reforms within the Church. The Council emphasized the importance of scripture and tradition as sources of authority and undertook measures to improve the education of Catholic clergy and curb their luxurious habits.