Poly bushings are harder (of course) than rubber. But, they also require more maintenance. At least once a year you'll need to take them apart and grease them. I'v had the best luck with Mobile 1
synthetic grease.
But, if you want the best performance, cut the bushings off and use a rod end. When I did that, I was amazed at the improvement in ride quality on the street. I don't know why more people don't do this.
