Answer:
Your answer would be a penny.
Step-by-step explanation:
Every other answer would have fallen slower because:
A large poster would work as a parachute (which falls slowly.)
A shoe box is empty and big, therefore would fall slowly due to the hollowness and size.
A cell phone is flat and wide (relatively) and would fall slower than the penny EVEN THOUGH it has more weight.
The penny would fall quickly, due to aerodynamics and size. It is small, has weight to it, and other contributing factors prove my point. :)