Polybush are the original and most common ( and expensive) manufactureres of polyurethane bushes. There's loads of other makes around too. I went for Polybush as in my opinion they're the best. Which rating depends on your application. They have three different compounds depending on use.
Someone else will be alomg soon to tell you to use a different brand.
I always prefer to go for the originals, not the ones copied by others.
Hope this helps!