The correct statement is: The substance with the lower pH has 1,000 times as many hydrogen ions per volume of water.
This is because the pH scale is logarithmic, meaning each whole number change on the scale represents a tenfold change in hydrogen ion concentration. Therefore, a substance with a pH of 3.0 has 1,000 times (or 10^3) more hydrogen ions than a substance with a pH of 6.0.