What is the most broken vow in the church?   The wedding vow?  Divorce rates among Christians are high, but rates of breach of this vow are probably higher still.   Ministerial vows to preach the gospel?  Conservatives in mainline denominations might point to those who are ministers and who deny key tenets of the faith from their pulpits week by week, though, ironically, such may not be in breach of vow if said vows do not explicitly bind them to uphold said tenets.   That's the dilemma faced by many in mixed churches today.  Baptism vows, to raise children in the fear and nurture of the Lord?   Doubtless there is much delinquency here.  Perhaps it is this one.

No.  The most broken vow is almost certainly that by which church members submit to the authority and teaching of the elders in the church.   It is as solemn and serious as any other vow one might take -- marriage, baptism, an oath in court -- and yet what does it mean?  How many truly think about the implications?  How many truly act as if the vow really meant something?  The vows are voluntary, but once taken, they are serious and require focused commitment and a particular pattern of behaviour.  Yet members feel free to speak as they wish to, and about, church leaders; they move from church to church as, so some say, the Spirit leads them; and they trample their vow to submit again and again.  When political parties enjoy more loyalty from their members, you have a serious problem; and don't gun for sports stars caught cheating on their wives when your own view of vows is at best selective in how they are honored.