I vote for Austin Racing RS22 because to me it sounds closer to the original 916 V-Twin sound, I guess because it is an exhaust with a long pipe and high undertail position.
From what my ear hear, the short FULL System Exhaust like Akrapovic or the SC-Project Full 4-2 sounds more high pitch than the Slip-On system like Arrow slip-On,
I believe this is because those short full system exhaust have a shorter length pipe compare to the slip-on with the longer stock exhaust manifold pipe.
The deepest sound I think came from the last ZARD Slip-On Ti (I think this is what
@DucatiKev use), most likely because it use the super long stock exhaust manifold pipe with big volume slip-on silencer.
Out of curiosity, I try to compare the SC-Project WSBK undertail exhaust vs. Austin Racing RS22, and at least from the YouTube video, the Austin Racing RS22 sounds deeper and again more like the original 916,
again maybe because the Austin Racing RS22 has longer pipe length and the pipe also looks larger in diameter.
Here is SC-Project WSBK:
Here is another video of Austin Racing RS22:
or
and
but I think the raciest sound is still this one: