I have a table with northern rubber and steel block cushions, i really love the response of the Northern high quality rubber (even though it's at least 10 years old). To share my opinion:
I have played on many pool tables over the years, and have yet to find a newer table with a desirable level of bounce response as compared to old tables with high quality natural rubber.
I own a 9ft pool table, and have replaced cushion rubber with Brunswick Superspeed cushion rubber, at a considerable cost at the time, it's been 8 years and i hate the way the rubber is responding at this point ( not even close to a natural rubber response- normally i would suspect a rip off, but i did purchase them from a very reputable online store).
I think you can't go wrong if you purchase Northern rubber, as long as you get the original, but i also think the cushions themselves make a big difference-
As an example there was a set of cushions for sale in England a couple of months ago, from a very reputable source (
http://gclbilliards.com) where the customer had the rubbers replaced with northern rubber, but after a year decided to switch into steel block (not happy with the end result- i think compared to steel blocks), and hence the newly recovered cushions were put up for sale at a considerable loss. I think they were posted for 350pounds, while the rubber replacement was at least that much.
Hope this helps.