Materials, and weight of the damper. It's a pretty advanced topic, (beyond the scope of my knowledge anyway) but the hardness and thickness of the rubber (or whatever damping material the manufacturers choose to use, and the weight of the outer ring are all critical components to the equation for a given combination. That takes R&D, precision measuring equipment and lots of know how. Companies like ATI and Fluidampr have lots of both. I can't speak for the other aftermarket companies, because I have never had their products, but if it is properly engineered for an application, I don't see anything wrong with using them. What I do have a problem with are inferior copycat products that end up using different (cheaper) materials and the quality of the dampening suffers. You get what you pay for! As far as the stock one goes. The rubber used in the ring is crap. It's pretty common occurrence for garage queen Corvettes to flip the belt off after sitting for a while then starting because the tension of the belt has pulled the damper off center just enough to cause it to run untrue. It happened to my father's vette, he had it towed to the dealership, he was expecting a week to get the parts, and they had 3 on the shelf. Service writer said it happens all the time to cars that sit. (In my dad's case 9 months while he was building a new house).