I have ridden with Grumpy, Stinger and IMOC with their different exhaust systems.
Not sure what IMOC has on, but it's much like the others.
To be honest with you there's not a lot of difference in the note or volume. They are all quite fruity and rather loud.
It's a bit like following three of the horsemen of the apocalypse, with me attempting manfully to keep up at the back on my old 900, into the wall of sound....
I think it would be down to the one you like the look of (and the price).