I now use Regular...
I ran premium (91-93 US Octane) for the first 3,000 miles after I first bought my bike, but have since switched to regular (87).
The reason I switched was I am often riding back roads in the middle of nowhere and have to stop at out of the way gas stations. In rural areas, they may not sell much 93 octane fuel, so it may have more water in the fuel.
That actually happened to me on a long road trip and it cost me a bunch of hours stopping and dealing with it before I finally got it all through the system (fuel additives with multiple fill ups).
I have not noticed my bike detonating, pinging or having a loss of power since switching.