Some food for thought when considering choice of bushings:
Polyurethane (poly) is normally firmer than rubber, and can give better control of the movement in some of the places we use them. It can also last longer than rubber.
Poly can squeak if not lubricated. Rubber can squeak if lubricated. (yes, this is true). The rubber bushings will stick to the surfaces and the material itself will give. I.e. there is no movement/friction between the rubber and the steel, only within the rubber bushing itself. Poly can not do this, and there will be movement/friction between steel and bushing, and therefore squeaking if not lubricated. Ceramic grease is good - doesn't wash off easily. Most poly bushings come with a small sachet of lubricant. If rubber is lubed, they will not stick to the steel, and start squeaking after a short time.
Another issue is that the bushings are there to make a flexible connection between two parts, some times in order to save other parts, by giving them less shock-load e.g. If the construction is designed for rubber bushings, it might not always be a good idea to replace them with something with less "give".
A sports-car mechanic/driver I knew (Monte Carlo veteran - RIP) said it very clear: He would normally never use poly bushings, because there would be something else giving in if the rubber didn't. And that's from someone who wanted maximum control!
I'm not warning against poly, just trying to highlight some of the considerations we can do.
Think of a sway bar: For the frame mounts it doesn't really matter how much they give as the bar itself gives a lot anyhow. But for the ends, there is a considerable angular movement, and the bolts will brake if the bushings are too hard or too thin. The only advantage of poly on the sway bar would be the durability of the bushings, as there is no advantage of restricting the flexing.
Hope I'm not littering the thread - The thread heading covers the contents....