How about the one that is unique and sincere from the one doing the praying. If you repeat someone else’s prayer it is no longer a prayer its a contemplative meditation.
Formulaic prayers, whether they are composed by the Saints or found in the Bible (Our Father, Psalms), and used by the Faithful, either in groups or as individuals, to express our love or give glory to God, are not considered to be “contemplative meditation”. So, your statement is a complete contradiction within itself. They might be used by some people to inspire their “contemplative meditation”, but they are not really a contemplative form of prayer at all.
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Meditation is a form of
mental prayer consisting in the application of the various faculties of the soul, memory, imagination, intellect, and will, to the consideration of some mystery, principle, truth, or fact, with a view to exciting proper spiritual emotions and resolving on some act or course of action regarded as God’s will and as a means of union with Him. In some degree or other it has always been practiced by God-fearing souls.”
Basically, what you refer to as your preferred type of prayer (“one that is unique and sincere from the one doing the praying”) is just another form of spontaneous mental prayer, or meditation. Catholics also use that type of prayer. In fact, the Rosary is a form of both of those types of prayer. It includes reciting formulaic prayers (Our Father, Hail Mary, Glory Be, etc.), while meditating on the lives of Jesus and Mary which we find in the Gospels. The main focus of the Rosary is Jesus, not Mary, which many Protestants fail to understand.
There are many different forms of Catholic prayer. We do not limit our spiritual exercises to only one particular formula or type of prayer. Every individual has their own personal preferences in regards to the ways they wish to communicate with God. The key to all of them is that they are used, first of all, to express our love to God, to give Him thanks for what we have already received from Him, and to ask for His help for our family, our friends, and for everything else we might need in our daily lives.