I think there is a large variety of resonators on the market and the materials used and method of construction obviously play a part in how well they work.
I have a 5inch 100 cell Venom cat, a 3in resonator about 500mm long and a 3in Japanese muffler ( had a job to find one that was 3in right through - many are stepped down to 2 1/2 in just before the tail pipe for some reason). This system sounds good and is right on the edge for legal loudness. This is measured at 3000 rev/min and its is in fact quite a bit louder at 6 - 7000 rev/min which is why i keep the revs down around town!