Which measurement is most accurate to describe the amount a coffee cup could hold?

Fluid ounces.

A coffee cup is a type of container that is typically used to hold a hot beverage, such as coffee or tea. The size of a coffee cup can vary depending on the design, but it is typically around 8 fluid ounces. This measurement is more accurate than milliliters or grams because it takes into account the volume of liquid that the cup can hold, rather than just the weight or mass.