The correct answer to this question really depends on your final design. What paramters are being controlled and what topology is driving the motor? (Type of the motor and Drive. Parameters: Position/Speed of the motor. Control algorithm: Speed Control/Torque and Direction Control, Current Limiting Circuit). If a general answer helps, then assume that you wanna control a dc motor position:
If you wanna increase the model accuracy and get closer to the real problem then:
The real world problem needs a very accurate system with more complexity.