When examining both options objectively, each has its own advantages.
The over method offers quick access to the paper and makes it easier to tear off individual sheets. Many people also feel it presents a cleaner and more organized appearance.
Meanwhile, the under method can reduce unnecessary unraveling. In households with cats, for example, a dangling sheet may encourage playful behavior that leaves paper scattered across the floor. Some parents also find that the under position discourages young children from spinning the roll.
Ergonomics can also play a role. Depending on the holder design and bathroom layout, one direction may feel more comfortable than the other.
Ultimately, the best choice often depends on personal preference and the specific needs of a household rather than any universal rule.