Atheists, what are the most convincing theist arguments you heard of?

[Whateverist]

For my money, the big bang cannot be the first ever cause of all time because you must explain how conditions could ever have reached such a compressed condition as well as what finally triggered its expansion.  Multiverses are the only alternative, unless you prefer supernatural origin stories.

While it is true that immediately after the Big Bang, the Universe was in an ultra-dense state, we cannot actually confirm that the Universe was in such a state before the Big Bang. Neither can we confirm that the Big Bang was, in actuality, triggered by something. All we know is that the Big Bang happened. It doesn't follow that the Big Bang necessarily requires a cause. Cause and effect are temporal phenomena, and time as we know it only began to exist at the Big Bang.

So we've been told but I question that.  Time within the phenomena associated with this bang only begins to exist as such at that moment.  But we have as little reason to believe that these phenomena are all that there are as we do to believe there are many such events.  That veil is very hard to peal back.  In the mean time an assumption on either side is just that, an assumption.