Atheists, what do you believe is the best argument for the existence of a deity?

[Mark 13:13]

The best arguement for the existence of God is personal experience; it may not convince other people but it sure as hell is much stronger than any amount of wonderfully crafted words and logic, if anything all the arguement really can act as a barrier to people really opening themselves to personal experience.

So when a serial killer says that god commanded him to commit his crimes we should take his word for it then?

Nope but if he really believed God spoke to him then trying to convince him otherwise will take some doing. Now Zen I'm going to challenge you with an extreme example and ask you to be honest and suspend your disbelief for a moment. If you were alive and an apostle of Jesus Christ and you watched him die on the cross and then met him again a few days later and chatted with him in the company of others and later again watched Jesus ascend into the sky. Could any evidence anyone try to give you that it didn't happen convince you otherwise, would you face death and still not change your mind?