For me it was a long, slow process to disbelief. I wanted to believe so badly because it was all I'd ever known. I couldn't accept the fact that my parents were wrong and that I had unintentionally been lied to. I took it that I was less intelligent and that as I grew and matured I would come to appreciate and understand the spiritual things everyone else I knew loved so much.
That never happened. I'm now 30. For the past 2.5 years I've been questioning everything, starting with our rich JW spiritual heritage and realized it wasn't as rich as I've been told. TTATT completely shattered my respect for the Watchtower organization, which led to an investigation of the Bible. That investigation led me to distrust the Bible as an authoritative source. This lead me to investigate the supernatural, which I found no basis for belief.
All my research led me to one conclusion: "The more we learn about science and the world around us, the more we explain religion away, and religion has to continue reinventing itself to stay relevant." Science has changed alchemy to chemistry and astrology to astronomy. I believe that early alchemists/witches/diviners/etc were people that had an early understanding of how to harness the power of some scientific phenomenon without understanding its true properties and cause, and therefore chalked it up to angels/demons. Phenomenon that was once used as a means for divination and mysticism have been explained away by science as having logical causes. When I think of religion and God, I see an early attempt of the human species to try and understand the world around them, and I think at the time it was a necessary stepping stone. Any hypothesis is worth exploring. However, once that hypothesis was shown to have no verifiable proof, it should have been discarded a long time ago. Instead, it lead to the real intellectuals and geniuses of our past being hindered and labeled heretics, hindering the scientific process, our technological growth, and our growth as a species. I truly believe that if religion hadn't got in the way, we'd be much better off today in all aspects of life.
As far as the Bible goes, I used to think (a looooong time ago) how could such a wonderful book be anything other than the word of God. Until I started reading the parts the Watchtower never highlighted on condoned rape, slavery, and other OT atrocities. And then I started reading the Book of Mormon and the Koran and realized it's easier to make this stuff up than you might think. They couldn't all be right, yet they had all done the same thing.