Metals are good conductors of heat and electricity
Metals are good conductors due to presence of free electrons
They act as carrier to conduct heat or electricity.
So
Aluminum spoon will heat up as it is of metal
Iron spoon will heat up as it is of metal
Silver spoon will also heat up as it is of metal
Wood is a bad conductor of heat. It is an insulator
Wood has air space or pockets in its structure which makes it a bad conductor (it cannot conduct heat)
So a wooden spoon will be stay coolest as it is an insulator