John 1:18
18 No one has ever seen God; the only God, who is at the Father's side, he has made him known.
Argument: Jesus is called the "unique God" or "only God".
This verse has both a contested translation, and a textual variant. Some manuscripts read "only begotten Son", others read "only begotten God". Then, there is controversy over how to translate monogenēs, with some saying it should be "only begotten", and others saying it should be "unique".
With respect to the textual variant, consider the context. The verse states, "No man has seen God at any time; the only begotten (Son/God), which is in the bosom of the Father, he has declared him". The reading "Son" makes sense, as it is referring to no one having seen God, and the Son making Him known. It makes less sense to say that no one has seen God, but the unique/only begotten God has made Him known. Likewise, the word monogenēs is very commonly (arguably exclusively) used elsewhere in the context of sonship/descendence (Luke 7:12, 8:42, 9:38, John 3:16, 3:18, Hebrews 11:17: 1 John 4:9), with the exact phrase "only begotten Son" being used of Jesus in John 3:16, 3:18, and 1 John 4:9, whereas monogenēs is never once used elsewhere to refer to God, or the uniqueness of God.
So, the use of monogenēs favors "Son" as the original reading. However, even if the variant is granted, it would still make more sense to translate monogenēs as "only begotten", rather than "unique". When the Bible says that there is "only" one God, it is the Father (John 17:3), and uses monos ("only"), not monogenēs.
However, if both the variant and translation favorable to the Trinitarian view are granted, the verse would still be distinguishing Jesus from God, and would be using a secondary sense of the word "God" to refer to Jesus, as it is used in Exodus 7:1, 21:6, 22:8-9, Psalm 82:1, 82:6, 97:7: 2 Corinthians 4:4, as explained by Jesus in John 10:33-36.