Final answer:
Copper is the best conductor type for flexible cables due to its high electrical conductivity, tensile strength, and ductility. Aluminum is cheaper but has drawbacks such as lower ductility and thermal expansion.
Step-by-step explanation:
The best conductor type for flexible cables is copper. Copper has the highest electrical conductivity rating among nonprecious metals, which means it can efficiently transmit electrical current. It also has a high tensile strength and ductility, making it flexible and able to withstand pulling and bending without breaking. While aluminum is cheaper than copper, it has lower ductility and tensile strength. It also has a higher rate of thermal expansion, which can lead to loose connections and fire hazards. Special techniques and designs are required when using aluminum conductors.