Not sure I've heard of many different aftermarket cats in general. RandomTech seems to be the main name that comes up the most often. I think that is what Bellanger includes in their kits, but I could be wrong. To my ears I really like the Borla kits. They have a deeper tone that is more reminiscent of a muscle car. The Corsa kits have a more exotic, higher pitched race-y sound to me. Bellanger I think is somewhere in the middle. There are quite a few others out there though. The Mopar race exhaust is more or less just a 3" version of the Borla kit (I think Borla makes it for them actually). Volume-wise I'm not sure I think there is a huge difference between them. They are all definitely louder than stock, but I think comparatively to each other they tend to be somewhat similar. I don't think I noticed a huge difference in volume with my headers either, though I did notice the sound was a little more "buzzy" than with stock manifolds (which are really just shorty headers anyway if you look at them).
Generally speaking though it's all personal preference. My cam made a bigger difference in sound than anything else I've done on my car exhaust-wise.
