Best answers so far:

Because the Bible is the only book on earth which prophesies its ending thousands of years into the future in its beginning (Genesis 3:15) and perfectly tells mans relationship with God while showing how the Messiah fulfills all of Jewish history in this relationship which lasts over thousands of years….all while telling the story through several different authors, over thousands of years.
The only person who knows the ending of the story when it is written is the author, and the author of the Bible is God, and his story outlasts generations and mans ability to conceive a story with such longevity. And the only person who could perfectly fulfill all of Gods covenants with man over millennia is God Himself in the flesh: Jesus Christ.
And if you say “the ending of the story was contrived to neatly fit the beginning of the story”: all of the men charged with spreading the fulfillment of the story (new Testament) died horrible deaths spreading that story and were martyrs except one. And he (John) lived to write the ending.
No other book on earth can claim this: multiple authors over thousands of years all telling the same prophesy, and showing the prophesy fulfilled to perfection with one man claiming to be God Incarnate.
Toni A

I think you look at:
— the holiness of the authors
— how the book was written/compiled
— the coherence, consistency, and reliability of the content of the book
The Quran is clearly written by someone who had familiarity with the Bible, but not enough to do it justice. And the earlier texts of the Quran blatantly contradict the later texts, so much so that a Muslim basically has to decide which ones they will adhere to. The earlier ones preach peace, the later ones violence. A book that is a complicated mess of forgery and contradiction can hardly be trusted.
Let’s look at who wrote it. Mohammad wrote the Quran. Islam’s own authoritative tradition shows him to be a thief, murderer, slave-trader, polygamist warmonger. He married a girl when she was 6 and had sex with her when she was 9. Yet somehow he’s God’s last and greatest prophet?
Now, let’s look at the Bible: The Bible is written by dozens of human authors over a span of thousands of years. Each author is an example of holiness, once they devoted their life to God (or Jesus). They’re not perfect, but they’re certainly not Mohammad. And even though the Bible was written by dozens of authors over a span of thousands of years, there is an amazing continuity and lack of contradiction. Christianity’s founder, Jesus, did not write any of the books, but we know from his life that He actually was perfectly holy. No child marriage. No slaughtering of entire nations and peoples. Just peace and perfect love.
Which book would you rather put your trust in?
Nick H