Dotsie, tools are good if you're going up against someone who tries to create a logical argument that "because of A, God must exist."
I mean, sure you can say, "You're full of it," but that's a bit ad hominem. Using logic to defeat logic has the potential to change minds, or at least to make a believer realize that there is no logic to believe in a deity, only faith itself. Which is absolutely fine. I have nothing against people believing what they want to believe.
Personally, my biggest logical argument against a believer trying to convince me that their God is real would be:
"If there truly is a deity, and your deity is the one true deity (or set of deities) who created the world and shephered your culture according to the stories you believe in, then how do you account for the thousands of other deities and stories that other people and cultures believe in? If there were only one true deity, then everyone would believe in the same creation stories and everyone would worship the same god. This is not so. Explain, other than saying that they're all wrong."
J-I-B