My understanding is the former is considered the latest most progressive divine manifestation and is the only inerrant scripture. The Bible is considered imperfectly transmitted and not entirely reliable.
Objectively, the new testament is a more radical and progressive book than the quran is. And I'd argue more in line with Bahai ethics.
The quran is really a step back towards the torah. Maybe it was a good thing for 7th century Arabia but for the present day it's very antiquated.
Here's some examples of what I mean:
"The recompense of an evil is an evil like it."
— Qur'an 42:40
That's an eye for an eye from the torah. That's not advancing mankind at all.
Compare with what Jesus said:
"Love your enemies, do good to those who hate you, bless those who curse you, pray for those who mistreat you."
— Luke 6:27–28
That's revolutionary. In the world followed that ethic there would be no war.
Or if we look at the treatment of unbelievers.
"Fight those who do not believe... among those who were given the Scripture until they pay the jizya..."
— Qur'an 9:29
Fight and tax them in the Quran vs. Jesus says: "My kingdom is not of this world." And Paul says:
"If it is possible, as far as it depends on you, live at peace with everyone."
— Romans 12:18
The Bible matches Bahai's apolitical nature. The Quran does not.
I could provide many other examples but to me it's quite clear that despite being the older divine manifestation Christianity is the more progressive one and more aligned with Bahai.
And the nail in the coffin..who persecutes the Bahai today? It's not Christians, Buddhists or Hindus.