The nature of atheism seems to me a side issue since the question I raised is about the best argument against theism. I talk about whether atheism is positive disbelief or just the lack of a positive belief, in this article:

https://medium.com/interfaith-now/do-atheists-have-or-lack-a-belief-in-god-ca7c674b9a5d?sk=1bb5b2b20b75eb4c367871eb57233794