In the late 70s, I machined Delrin suspension bushings for my car…they got beat out in no time (like several months). For that reason I keep away from hard plastics like Delrin and Nylon. Polyurethane is a great material, but if the lubricant gets washed out (or don’t get lubricated at all), they will squeak and drive you nuts…it’s like having an annoying cat in your trunk. Once you get into the hard plastics (Delrin, Nylon, Polyurethane, etc.), I bet you won’t be able to tell the difference in added road noise in your car from the ball joints. Go with the ball joints (Sector111, Nitron) and do it right. I got Nitron’s for mine.