Powerpark- There are now Six Major Tire Companies out and if i am correct they use pretty much the same foam.
All of the above are high quality tires and you can't go wrong with any of them. Some prefer one company's wheels or slight durometer rating differences to another but they are pretty much the same. Something else to consider is that I've heard different people have had different experiences with tires even during the same season!
Now some other High Quality Tire Companies that come to mind but are not necessarily easy to get in the U.S. are:
I THINK (not sure) that maybe one reason that nitro tires cost less than standard carpet foam tires is that "some" of the nitro tires may be the "Class A" family of foam that has a LOT of natural rubber in them but as a result they don't generate as much traction maybe, especially on carpet.
Shore ratings tell you softness but they don't tell you the differences in grip characteristics that you might experience between different "families" of tires. You may want to read the T.M Tires thread for some info and also the CRC thread, they have an excellent article about tires.