Let's split the case a little bit.
1. What are the possibilities that God exists as a higher intelligent being?
2. What are the possibilities that God is as described in the bible?
For the moment let's treat those cases completely separately.
As for #1, it is just as much probable as improbable (for me). The only logical conclusion anyone can say for sure is "We don't know". We can lean towards one or the other side depending on how we see things, but we have no ultimately proof, or evidence that can lead us to proof (evidence that is a theory we can, but haven't yet proven, so that we make necessary scientific reaserch to prove it). I hope you can agree with me on this one. Unfortunately, for me, the argument that everything "looks fine tuned" is not an argument at all. How something "looks" is just your perception, which might be true, but on the scale of the universe it is highly probable that it's just your way of pattern recognition. Now, using this to support other arguments is futile. Even if we could, we cannot calculate probability on this one. At best it's 50/50.
As for #2, it's all in the matter of probabilities, not certainty. (I belive that given enough time you could show definite proofs, but I don't feel like I'm the one person with capabilities to do that.)
The Bible is words written on paper in the form of book. Some of the stories were written after passing it down over generations from parents to children.
First we assume that having no other proof of this one particular god (miracles, sightings etc. can't be used as evidence, because they can be made by any god actually including the theory about prankster god which places the evidence just to mess with us, and that it all might be just our false pattern recognition thing which is scientifically proven not only to exist, but that it is actually a very common thing over billions of years not just in humans but in all animals as well).
So the only way we know this is THIS and NO OTHER god is in form of written word.
How many books humans wrote up to, let's say AD 1000 (roughly)? My answer: REALLY large amount.
How many of these stories were untrue stories, and this can be proven given the knowledge we have today? My answer: Most of them.
Why?
Some books were written just out of pure fantasy.
Some books were written giving theories which people couldn't prove false because of little technological advancement.
Some, actually most, books were burned because people disagreed with the ideas inside of them. And given the historical data (from different sources), it is the Christian church who did much of the book burning.
The most Important Thing: The books were EDITED. It Is extremely hard for historians to get books in their originals, because it is proven that censorship existed all the time in different forms. Data sources were cut, reassabled, changed, etc,. to fit the current ruler (be it king, pope, or just simply a mad scholar) point of view and/or ability to control people/earn money. We do have more and more evidence (supported) that Bible was edited many many times since the first writings. (Even if some of them are false there is a vast ammout of many more that still holds up.)
You can ask a question: But you have to belive in something.
Yes. BUT. First Question I Ask is: "Do I Exist?" The best bet for this is Yes. And... It's still a bet. I don't know, I may not be alive, I can be f.e in matrix. But If I don't bet this one I cannot do anything so I AM BETTING this.
Next Thing is: I have to somehow interact with data given to me (by people or by what i see/hear/smell/touch).
Problem is: People can lie to me, and my senses can lie to me as well.
But same here: I have to bet on something. I would first bet on my senses though. If I see something red, it would be red for me until somebody would give me proof that I cannot disband in any way. A proof that If I would not accept, my bet on "I do Exist" would crumble.
Next I estimate of how much people (different groups) lied to me/told me the truth/showed me the evidence WITHOUT my judgment of if it makes me happy or not. (The worst truth is still better than a beautiful lie.)
Now I have sciencists whose doctrines (in my view) are: We don't know many things, we'll try to figure out the answers, if somebody, even one of us will get an idea, we will do everything we can to proove whether it is right or wrong. Every hypothesis that you cannot prove false is good as a hypothesis, but should stay a hypothesis until the evidence is found. (Remember, I'm still talking about my point #2 here, not 1.)
Many of them were wrong, but in the end there were other sciencists that proved them wrong.
What they always told me was: This is true and you can prove by doing this experiment. It will work always that way whether you like it or not. Just deal with it. You have questions about how it works? Here, here are the explanations. Black on white, always the same, no metaphors whatsoever.
If an idea is tested long enough and provides enough evidence to support it from different fields of studies by different people all around the world, and it's stripped of logical fallacies, it can be considered true. No other sciencist coould contradict them without giving proper mathematical evidence that it may not be true, bacause that's what we as human beings consider being a lie.
On the other hand there were religious people. Many religions, many different worldwievs. Every single one of them claiming there is only one god and he's choosen only them as the choosen nation. When asked for evidence about it the only one that couldn't be viewd as fallacy or stupidity was pointing towards holy books (Bible, Koran, etc.)
First Problem is: All books are man made. There was nothing that implied that they COULDN'T be man made. Now the probability check: Is it more probable that those books are simply another book written by man, like thousands before, or that it is a work of people influenced by a being FIRST TIME DESCRIBED ONLY IN THIS ONE BOOK?
I could see a fallacy here. If I write a book, say that everything included in this book is a work of magical tea pot, that it influenced me to write this book to show everyone on the planet that it exists, then wait a few hundred years, nobody could prove that it is false. Yet this would be a perfect tool to control people. It WOULD work. And seeing the number of different religions in the world is evidence enough to support this idea.
At this point I was sceptical but I still didn't have the certanity. Then I actually started reading the bible. Now I coud see that there are many things that you can take literally, but if you took the bible literally as a whole, you couldn't exist in our world anymore. Those laws were perfect for people 2000 years ago in that particular area, but most of them were nonsense right here and now.
Then I heard: "Oh, It's metaphorical", "Oh, it's just Old Testament, read the "New one", and "You can't say what Jesus taught was wrong."
The problem was: On each and every single one of them you could find some contradictionary idea that you couldn't prove wrong (without the bible) either.
The main problem seemed to be morality. Each religion gave the same: "We teach morality, other's don't". The problem was weird because most of morality rules in each religions are the same.
This leads me to ask a question: Which was first, morality or religion?
And though it appeared to me that if moral rules were developed first, spread across the globe, you could very easily use them to make a new religion.
Now there is one more thing that told me this may not be true. Every time a person had seen something extraordinary, "This must be God's doing" was stated, UNTIL the moment somebody could prove that it is actually normal physics laws.
As history and my own senses showed me my whole life, every beliver sees god ONLY in things he/she cannot explain. Once is explained there is no supernatural power in this particular thing, thus shrinking the biblical miracles of killing entire nations to appearing on toast.
Getting back to the Bible:
Given this, and what science has told me, If I belived right now that Genesis happened EXACTLY as it is written, would contradict indisputable evidence that science provides.
If I have to take it METAPHORICALLY I can't be sure that any other thing in bible, including "love thy neighbour" isn't a metaphor. I don't know that the existence of Christ isn't a metaphor. I can't be sure that whole bible isn't a metaphor. And there is no experimental way to determine what should be taken as metaphor and what is not. Given that every person can interpret it on its own in its own way, that leads to no actual knowledge from the Bible, just one person's personal thoughts fit into a metaphor which you can find refferences to it in the Bible and it can be anything, even killing. That tells me that the Bible, in this case, even if true, is useless.
Now there's a third option that Bible is not a work of supernatural inspiration.
Can it still exist even that there is no god? Yes.
Does it still make sense that people belive in it? Yes.
Can it still show good moral behaviors despite of nonexistance of biblical god? Yes.
Can it be used to control masses of people? Yes.
Now, I had my answer.
For me it is enormous evidence that Christianity (and other religions as well) are just man-made, grown on different ideas with already existing morals as "food for people", mostly using to gather same groups of people and control them.