Consider two epistemically possible worlds that are as similar as can be, except that atheism is true in one world and theism is true in the other world. Which world is it rational to prefer? I explore the strongest defence of the somewhat counterintuitive claim that it is rational to prefer the atheistic world. I also discuss the opposite conclusion, namely, that it’s rational to prefer the theistic world. Surprisingly, my conclusion is that it’s difficult to tell whether to prefer theism or atheism overall.