What is the best scriptural evidence against the doctrine of the Trinity?

Perhaps John 14:28, where Jesus says, "The Father is greater than I". It would certainly seem to contradict the Catholic doctrine that the Son is co-equal with the Father.

Mark 1:9-11 records the first of three occasions when Jehovah spoke from heaven.

Jehovah said: “You are my Son, the beloved; I have approved you.” How it must have touched Jesus’ heart to hear his Father’s voice expressing love and reassurance to him! Jehovah’s words confirmed three important facts about Jesus.

 First, Jesus is his Son. Second, Jehovah loves his Son. And third, Jehovah has approved his Son. By saying “You are my Son. 

There is none.

The strongest evidence is in interpretations of Bible verses about Jesus and the Holy Spirit as in the writings of non-believers in the Trinity doctrine, such as Unitarians and Jehovah's Witnesses but with the JWs, they have changed the Bible at those verses in their New World Translation, proving their 'evidence' is utterly corrupt. It also shows how desperate they are. They also misunderstand the Trinity doctrine (as do Muslims, Hindus and others), misrepresenting it. That's called "setting up a straw man argument" - one they can then easily knock down. Readers, beware!

Nothing, NT confirms and OT insinuates. 

Philippians 2:5, 6: "Keep this mental attitude in you that was also in Christ Jesus, who, although he was existing in God’s form, gave no consideration to a seizure, namely, that he should be equal to God."

1 Corinthians 15: 23-28: "But each one in his own proper order: Christ the firstfruits, afterward those who belong to the Christ during his presence. Next, the end, when he hands over the Kingdom to his God and Father, when he has brought to nothing all government and all authority and power. For he must rule as king until God has put all enemies under his feet. And the last enemy, death, is to be brought to nothing. For God “subjected all things under his feet.” But when he says that ‘all things have been subjected,’ it is evident that this does not include the One who subjected all things to him. But when all things will have been subjected to him, then the Son himself will also subject himself to the One who subjected all things to him, that God may be all things to everyone.

"Trinity" is not a Bible word.

There is no scripture that speaks against the teaching of Jesus Christ, Who repeatedly spoke of the three Persons of the Trinity, both individually and collectively.

Mat. 19:17 .*************

The best scriptural evidence is that the Trinity is true.