The statement that best describes an informal argument for the formula for the volume of a cylinder is:
"A cylinder is a stack of h circles, each with an area of πr² and a thickness of one unit, so its volume formula is V=πr²h."
This correctly represents the volume of the cylinder as the area of the base (the circle) multiplied by the height (the number of circles stacked), which gives the formula \( V = \pi r^2 h \).