Forget evidence, how about common sense?
When debating atheism vs. theism it's almost always about how one side uses evidence and how the other uses faith. Obviously, as an atheist this should be enough since it's...rational. However, if our goal is to turn people away from religion, perhaps more practical approaches could be exercised. Below I break down the qualities/properties of the Christian "God," and briefly explain why it's foolish to believe.
There's no way to metaphysically identify the properties of a God so I will just relate what the Bible describes to that of the physical universe.
1. God is Omniscient: (God is all-knowing)
-- If "life" is supposed to be some sort of trial for humans to endure, why not just hit fast forward? If God already knows the outcome of our mortality, why does he need to let us figure it out on our own? It's not like the life experience will benefit the person once they go to Heaven or Hell, and no matter which place they go to, he would already know beforehand. So, life must be some sort of experience for God, as well. If our existence doesn't matter to us (because we shed our physical bodies when we die, returning us to our "spiritual" existence), and it doesn't matter to God (because he already knows the end result), then the experience of living must be some sort of form of entertainment, education (making God not all-knowing), or limitation for God. After all, should the collection of life choices we each make from the day we're born till the day we die, REALLY determine our eternity? That's like saying the Cardinals were destined to lose the Superbowl last year if they lost the opening coin toss. That leads me to the next to property of God.
2. God is Omnipotent: (God is all-powerful)
-- If God is forced to let our lives carry on this futile existence because he's too limited to hit fast forward - or skip the whole "Adam & Eve" Chapter, then he is not all-powerful. I think I can skip the endless calamities that plague our species like cancer, war, Bill O'Reilly, etc...It's unbelievably easy to prove God isn't all-powerful, whether he exists or not.
3. God is Omnipresent: (God is all places at once)
-- This one has always seemed self-defeating to me. If God is omnipresent, he knows what is always happening and if he chooses to let bad things happen while having the ability to stop these things, he's immoral. The argument that God doesn't interfere because every person is to be judged when they die means that when things do go horribly wrong, his ability as a creationist has failed. It really doesn't matter what the circumstance is, all actions, thoughts, feelings that we all possess, stem from the creation of a perfect being (assuming you believe in said being). Same applies to the planet. So if God knows what all the problems are across the planet, at all times, and they aren't prevented, he either doesn't care or he's imcompetent.Both disqualify him as God. Or at least, the Judeo-Christian God.
4. God is all-loving:
-- This one is laughable. Besides the pain and suffering our species as endured, by his own words (via the bible), he LOVES hate. In all forms.