In programming a robot, which command would effectively stop the motors?

Setting motor power levels to 0 is the most effective way to stop the motors because this command directly instructs the motor controllers to halt movement. When you set the power level to zero, you effectively disengage the motors from driving the wheels or any connected mechanisms. This is a straightforward and efficient approach that ensures the motors come to an immediate stop without any residual motion.

While options such as using a wait command may pause execution, it does not influence the motor's operational status. Calling a stop motors function could be nearly equivalent to setting the power levels to zero, depending on the implementation; however, the direct method of sending a power level of zero is often clearer and more immediately understood. Running motors at negative power levels would not stop the motors; instead, it would reverse their direction, potentially causing confusion or unwanted movement.