I did.
But you're right, more rational is what I should have said.
You're better off with "more likely". Neither theism nor atheism is irrational. Hell, solipsism, brain-in-a-vat-ism, the theory that we exist in a computer simulation, etc. are all rational theories. They all could be true.
Atheism and theism are simply competing theories. Your best bet is to show, by a Bayesian calculus, that atheism is confirmed to a higher degree than all other competing theories by the available evidence. I don't think you'll be able to do that.