Nothing wrong with written prayers; only with mandated written prayers, or written prayers which become a formality without heart worship.
We have the Westminster Directory for the Public Worship of God, which offers helps on what should be prayed for in public and family worship; not prayers exactly, but suggestions regarding the content of prayer.
Also, the Book of Common Prayer (I often use the Reformed Episcopal Church edition, as it is more Protestant) can be adapted for personal and public prayer.
Use of the WDPWG directions, or a the BCP, can help us learn to pray. Too often public prayer is anemic, not biblical, and neglects the concerns of the first three petitions of the Lord's Prayer. Read the Larger Catechism's sections on the Lord's Prayer for a good list of prayer concerns.
Prayers written by committees are often terribly written; but the BCP is a wonderful example of English prose.