None of the above. There were some accurate observations made, but none really smacked it home as they were incomplete.
Fans work by the blades movement creating a low pressure area in front of them. Faster the rotation, stronger the vacuum. The byproduct is a pressure wave out of the back of the fan.
With that, exhaust fans work by creating a low pressure area, and nature abhors a vacuum, so the higher pressure air supplied at the front of the case will physically move to fill the void created. That's airflow.
So you do not want low pressure areas in unwanted or competitive positions, such as anywhere near the cpu cooler fan intake. You will want as much low pressure as possible on the cpu cooler exhaust.
That means only One fan on top, as close to the rear exhaust as is possible, doubling the potential low pressure area, so more air is moved, faster, from front to rear, which has the side affect of feeding more air to the cpu cooler fan, which also has an easier time pushing its air through as there's a stronger vacuum at the rear.
Might not be as pretty or as balanced looking as having 2 fans on top, but it works far better, especially under higher load outputs, which lowers temps everywhere.