Does God exist: A hopefully civil and fruitful debate

EDIT: [MENTION=4093]SaptaZapta[/MENTION]

Define "God".

If you want to discuss something with perfect rationality, first you must define it precisely. Then we can apply logical rules of deduction to prove its existence or the impossibility thereof.

I'm talking about the omnipotent, omniscience and omnibenevolent being. I'm not entirely interested in his Catholic teachings, or the teachings mankind attributed to him, or the whole history of Jesus Christ.

I think we haven't had one of these threads ever since this subject got the green light from Eos, so let's give it a try.

Some things to keep in mind for the sake of civility and intellectuality.

• A person's stance need not be his own belief. There are two ways to argue: emotionally and rationally. We strive for the latter here.
  
  
• Be mindful that while one may fail to present a proof for his cause, it is still sufficient for him to defend the proposition so long as he had provided an argument for it to get things rolling (burden of proof). Things may not get resolved, but keeping it going until we get the most rationally defensible position would be acceptable, even desirable.
  
  
• Be critical and try to separate things that are usually lumped together, although help should be provided if you fail to do so.
  
  
• Added: Be clear about your idea; we aren't all inside your head. Try to develop a clear picture of your position and present it in as much detail as possible.

[*]Added: Since it is supposed to be a debate, please, to the best of your ability, justify your claims rationally.

I usually like to play angel's advocate (as there is a lot of criticism from the atheist's side), but for now, I'll borrow someone's point of view to get things going.

Also, evidence doesn't prove anything. It lends support to arguments concerning what is most likely the case.
Proving doesn't leave the realm of mathematics.
While I very well know I can't ask for evidence, let alone proof, of God, the absence of evidence is telling. God arises from unanswerable why and how questions. That doesn't do anything.
If God is as he is described in the bible, for example, he has mutually exclusive characteristics. He cannot be all good, all knowing, and all powerful with these results. Therefore, he is a contradiction. I will not look further than that because the argument of the bible unravels at the beginning.

A typical argument. How would you respond?

EDIT: To make things more concrete, I'll borrow the famous argument from evil as an instance of said 'contradiction'.

If God is omniscience, omnipotent, and omnibenevolent, then whence comes evil?

Break-down:
- If God is all-knowing, he must be aware of evil.
- If God is all-good, he must be willing to stop evil.
- If God is all-powerful, he must be able to stop evil.
- So there cannot be evil in the world if God is all-knowing, all-good and all-powerful.
- But there is evil in the world.
- Therefore God is either not all-knowing, not all-powerful, or not all-good.