How plausible do I find it that God exists? Well, “God” is a poorly defined term, corresponding to many different ideas. Let me recast the question in terms of some specific hypotheses. (There’s a peculiar idea floating around that to qualify as an atheist, you have to have decided beyond all possibility of further argument or evidence that there can’t be a deity. The people who offer this definition are projecting their own faith-based mode of thinking onto others. Atheism is non-acceptance of the existence of a deity, not non-consideration of arguments for one.)
Could an intelligent being have created the universe? A cheap way out is to answer that the universe is everything that exists, so no creator can lie outside it. But let’s take “universe” to mean the space-time bubble we know about, the limits of the remnants of the Big Bang and of what the best instruments can detect. There’s no telling what lies outside it, if anything. I find the hypothesis that an intelligence created it less implausible than the one that it just popped out of a fluctuation in the vacuum state, which isn’t saying much. But it’s all a matter of idle speculation; there’s no convincing evidence for or against it.
Could this intelligence be one that knows about every detail of the universe and can intervene at will? This is much more of a stretch, but I can’t rule it out a priori.
Does this all-knowing, all-powerful intelligence care about the inhabitants of our planet, and does it purposefully allow so much suffering that can’t be attributed to anyone’s choices? That just doesn’t make sense.
Does it care about what people think of it, and does it reward and punish people eternally for their beliefs and religious practices or lack of them? That’s insane.
Did this being create everything from the planet through the human species in six days, plant consistent evidence to the contrary, drown almost the entire world’s population, kill tens of thousands of Egyptian kids on account of their Pharaoh’s policies, enact death penalties galore, and order the massacres of Jericho and Ai? There are limits even to insanity.