I don't know what the Sumerians genuinely believed - I don't accept anything Erik von Daniken might have invented or promoted - but even if I believed in God I still regard those ancient myths as of no more than historical interest.
Neither idea has any concrete evidence that it is true. "Ancient Astronauts" is based upon a crude hoax by Erik von Daniken that was discredited in the 1970s. ETs cannot travel from star to star for several scientific and mathematical reasons. No ETs were ever on our planet, and none will ever be here. The Bible is so full of foolish errors that it shows God does not exist.
I wouldn't go so far as calling them "foolish errors" but obviously they cannot be regarded as "true" despite some modern Flat-Earth types wanting for their own reasons, us all to think them so merely by being in a particular book.
The whole book is no more than a rough-and-ready anthology of the beliefs and customs of a society occupying a relatively small region of the Middle East some 2000 - 3000 years ago, in their Late Bronze Age to the Roman Occupation. The beliefs may have been held sincerely, but I agree that is no proof either!
So essentially, the answer to the original question is simply, Neither!
Benedict Arnold 