Most travel pillows fail the same way: they're soft enough to feel nice in the shop and useless three hours into a flight, when your head has tipped forward anyway. The ones that work are firmer than you expect and support the side of the neck rather than the back.
Our memory-foam pillows hold shape under load and recover between trips. The inflatable options pack down to almost nothing and are the better choice if you're travelling carry-on only or want something for a bus or train rather than a long-haul seat. Several models include a chin or side support, which is the part that stops the forward tip.
All of them compress into a pouch and clip to a bag strap, because a pillow you have to carry in your hands tends to get left behind.