Theists: What is the most compelling argument you have heard for Atheism?

[Angrboda]

The evidence that I believe that supports my belief (another opinion) is below:

1. Person of Jesus is compelling.
2. The NT describes actual events including the miracles, life, death and resurrection of Jesus.
3. God works in people's lives today--changing people on the inside as well as the occurrence of miracles.
4. The natural theology arguments:
a. God is the best explanation why anything at all exists.
b. God is the best explanation of the origin of the universe.
c. God is the best explanation of the fine-tuning of the universe for intelligent life.
d. God is the best explanation of intentional states of consciousness.
e. God is the best explanation of objective moral values and duties.

Since you cannot 'prove' that any of these are falsely held beliefs, my conclusion (opinion) that God exists is rationale. The amount of evidence meets my personal threshold for proof that God exists.

Hey, they're your beliefs, your rationale and your thresholds.  You could tighten them up or make them a lot looser and my opinion would matter just as little.  They only have to please you.

But I have a question for you.  Why do you assume in your "natural theology arguments" that all these functions are performed by just one being? [1] All of them assume that external agency is required, something I find more dubious than satisfactory in explanatory power.  But even if you hang on to a tinkering mega-agency as being required for a-c, why couldn't d-e be explained by evolution or as unintended by products of a-c?  [2]

Funny how the impulse to keep it simple by attributing it all to just one omni-agent doesn't go even further and leave out the middleMan altogether.  Instead of everything is just so because it is the will of God - where the will of God just is the will of God, you could have everything is just so because the universe just is the way it is.  Simpler still. [3]

1. The arguments are not conclusive on their own. They are part of a cumulative argument for the existence of God. Separating them out and positing different entities is an unreasonable step (there is no reason). 

In a cumulative argument, one result is dependent upon the prior result, and so on. These are all independent lines of evidence: none of them reinforce each other. What you have is what is known as a 'rope argument' in which the independent strands are woven together to make one argument. In a rope argument, the whole is only as strong as the strongest individual strand. And in your case, none of the individual strands are particularly strong or convincing. So what you actually have is a weak argument.