High octane gasoline is not "better" than low octane. It
is better at preventing detonation, pre-ignition, ping, spark knock, whatever you want to call the explosion inside the combustion chamber instead of the controlled burn we should have.
As Gort said, use 87 when cool and 91 or 92 when very hot. There is no point using mid-octane gasoline.
Stimpy kind'a has things backwards. Lower octane is OK at high altitude in engines without knock sensors, thus the availability of 85 octane in the Rocky Mountain areas with less dense air containing less oxygen. (For more advanced engines than our Suzukis, use the octane level recommended in your owner's manual. All automobile engines after 1986 are more advanced than our bike engines!)
Better brands of gasoline do have better additive packages for competitive reasons. The EPA establishes minimums, but some gasoline marketers exceed these minimum standards.
http://www.toptiergas.com/.
Here on the West Coast BP's ARCO brand has the worst gas I've found. The gas mileage in my car & truck with ARCO are noticeably worse than with any other brand including no-name supermarket gasoline (Which is often Tesoro here).