To bring this into line with the OP, I will add that the Christian does go one step further. She will, presumably, assume that her god created the universe, and that this god itself requires no creator.
Now, logically, it's no more nonsensical than assuming that the material universe in which we live requires no creator; no is it, in my opinion, no more nonsensical that there is a certain number (perhaps infinite) of prior creators. I don't buy the notion of a transcendent First Creator mostly because I see no evidence that one exists.
On the other hand, I do agree that the notion that God is transcendent and created time and space ex nihilo is extra-Biblical.
The question 'Who created God?' then boils down to 'why is it necessary for there to be a God?' It can be argued consistently and rationally that nature can be assigned the status of an ontological self-sufficient causal generator, not an effect. What is responsible for this causal generator then becomes a meaningless question. As in an axiomatic system, axioms are statements that generate the proofs, they are not things being generated. They require no proof.
The problem for the Theist using this line of reasoning to establish God as Ontologically fundamental is that they assign God numerous anthropomorphic attributes -- intelligence, emotion, will, reason etc. These things are all parts of the causal machine we are subject to here in the temporal world. If God possess such properties he is also subject to casual mechanisms - thought and reasoning proceeds in an orderly and timely manner etc. One can then state God is not fundamental and ask from what ontologically prior causal generator gave rise to these mechanisms?
To avoid this quagmire, one can certainly dump all of those anthropomorphic properties we assign go God. We then end up with something akin to this concept of nature - a causal generator and nothing more. What rational reason is there then for assuming the existence of a rather redundant extra step in the food chain?
This certainly is not a proof or argument that a God does not or cannot exist. I am thoroughly Agnostic. But as noted above, it may help more than hurt the popular theist position and that is probably why it is seldom used. Perhaps a rational argument can be presented by theists that offers a way around the problem, but unfortunately, as the OP states, many are too preoccupied with using circular attempts at answering the questions.
Using scriptural texts as self-validating(e.g. God exists because the Bible says so and the Bible is true because it's the word of God) certainly can be a faith-based initiative, but in this forum or in public discourse it's kind of like showing up to a gun fight with a knife.