I keep it simple: I use premium because I can get it in Wisconsin without ethanol in it.
Ethanol blows, for more reasons than we're gonna wanna discuss here, and if I can find a way to nit use any of the crap, I won't.
In this case, most of the performance and mileage increase is because of the pure gasoline rather than the octane rating. Gasoline has about 33% more energy by volume than ethanol so switching from an ethanol blend to pure gasoline (even at the same octane rating) will give you an immediate improvement. Often the difference is enough to be noticed by the "butt dyno".
The trend lately has been for more and more gas stations to offer a non-ethanol grade because it is much better for small engines like motorcycles, boats, lawn mowers and generators. It is usually offered at separate pumps as a mid-grade 89 octane but some are premium and a very few are regular 87 octane. Just be aware that it may not come from the same supplier as the ethanol blends sold at the same station. It may not even be branded or top-tier fuel. Generally, if it is offered at all of the pumps as their higher octane (e.g. all premium at a station is non-ethanol while the other grades are E10) then it is their branded fuel. But if it's only offered at one or two separate pumps then check the labeling carefully to determine if it might be unbranded fuel being sold as a convenience.