As stated in the previous posts the rubber is a softer compound than the poly. Therefore, there's more potential for sloppiness in the components if you use rubber. However, poly has been known to squeek. My brother in laws Blazer was terrible after he redid his suspension bushings in poly (could just be because it was a Chevy product...). There's also polygraphite and midolyne manufactured bushing now that are suppose to be hard like regular polyurethane, but be self lubricating.