Greetings,
PCIII USB is my vote, here's why:
The Air/Fuel map stock and on all PC models before the USB sets the Air/Fuel every 500 RPM.
The PC III USB sets it Every 250 RPM, that's TWICE as often!
Put a PC III USB on a Bone Stock Busa, with a Stock Map loaded and it will run twice as smooth.
Naturally modded bikes just magnifiy the benefits. I upgraded from a PC IIIr for this feature alone, Worth It!