Price-wise, the S8 is probably best bang for the buck. You should always use premium on your bikes, it's not like you're filling up a Hummer.
I have never used premium in any of the bikes I have owned except my R1100GS which required it. When you pump premium from a gas pump with only one hose, the first quarter gallon or so may be regular. Not a big issue in a Hummer but when you only have a small tank to begin with, you will seldom actually be getting premium. You will get a regular/premium mix. Also, if an engine is designed to run on regular, premium will not make it run any better. Premium has no more energy than regular, it only resists detonation and pre-ignition better.
What does the owners manual call for?