Toilet paper should be hung so that it unrolls towards the front (over the top of the roll).

Although this is one of the internet’s most heated debates, there are two pieces of irrefutable evidence that settle the matter once and for all.

Evidence from an 1891 patent
The strongest confirmation comes directly from the inventor of perforated toilet paper. Seth Wheeler patented the toilet paper roll in 1891, and his official patent drawing clearly shows the paper hanging over the top of the roll towards the front.
Hygienic and practical reasons

Orienting the paper towards the front is not just a matter of aesthetics, but primarily of hygiene:
Fewer bacteria: When the paper hangs towards the front, your fingers touch only the sheet you are actually using when tearing it off. If the paper hangs towards the back (against the wall), your knuckles and fingers inevitably rub against the wall or tiles, transferring bacteria to them.

Easier to find the end: The end of the paper is more visible and easier to grab.
Folding into a point: This method allows for the decorative triangular fold often seen in hotels.
The only exception: Households with cats and small children

Hanging the paper towards the back (behind the roll) has only one practical justification: if you have a cat or a small child at home. If a cat bats at a roll hanging towards the front, the paper unspools endlessly onto the floor. If it hangs towards the back, the roll merely spins in place when struck, and the paper stays wound up.

However, in terms of history, design, and hygiene, the forward-facing orientation is the only correct one.