The M102 4 cyl is the original powerplant for the W201 and the chassis was engineered for it. The M103 6 cyl was shoe-horned into the engine bay to provide a platform to compete with BMW's six cylinder sedan. With more torque, HP and performance close to the 2.3-16, the M103 is great for freeway cruising. From a maintenance point, it's a lot easier working on the M102 than the M103, especially up front.