A metal surface would give the best radar echo due to its high reflectivity to radar waves, which makes it superior for radar detection compared to wooden, glass, and plastic surfaces.
Out of the given materials, a metal surface would give the best radar echo. This is because metal surfaces are highly reflective to radio waves, which are what radars use to detect objects. Materials such as wood, glass, and most plastics tend to absorb radar waves to a certain degree and do not reflect them as well as metals. For instance, small boats made of fiberglass or wood are not readily detected by radars, necessitating the use of radar reflectors to make them visible. Additionally, the design considerations for stealth aircraft include avoiding reflective surfaces such as 90° corners to minimize radar detection.
So, the metallic surface is the most effective for reflecting radar signals, making it the superior choice for a radar echo out of the options provided.