Which material is better? As with most material selection questions, the answer is
“it depends”. Both materials have their place but which material is actually superior?
In the case of tires, seals, and some belts, rubber is the best material. In the case of bushings, spacers, and high load components, polyurethane is the better choice.
Polyurethane has higher abrasion, cut, and tear resistance. It can be made in a higher hardness rating and it has better load bearing capacity. Polyurethane is easily colored, in some cases chemical resistant, and much easier and cost effective to mold into shapes and sizes.
Rubber by its soft nature allows for the absorption of vibrations and noise which may give the assumption that polyurethane isn’t as good for vibration dampening but polyurethane is also an excellent energy absorber and can be made in very low durometers.
In most cases polyurethane outperforms its rubber counterparts in replacement of many components including; bushings, pads, and many others. The parts will last longer, standing up to chemicals and oils, and compression and load. Finally, polyurethane looks better than rubber. In some cases this will not matter but a polyurethane part will always look much better than its rubber counterpart.
So in the end if you are going for performance and quality, choose polyurethane.