I would think God could do a much better job than that, and write a book that doesn't lead so many people to opposite beliefs and interpretation.
Agreed.
What are your reasons for believing the Bible is the word of God?
Well, you just gave my reason for believing that the Bible is NOT the word of any god. It's internal contradictions, unkept promises, failed prophecies, moral and intellectual errors attributed to a perfect god, and its errors in science and history tell you that the book was written by people unable to do better.
Said another way, I am asked to decide if the author(s) of that book also designed and created the universe. Just look at them both for your answer. Isn't that a bit like asking whether the author of misspelled graffiti sprayed onto the base of a bridge is the same as the designers and creators of the bridge?