well, if you think environmentaly , to save energy, save nature, save car parts, get higher performance, less emissions , then use higher ocatne or super.

but if want to be less freindly with the envirnmont use less octane number which is the premium.

there are actually fuels which are more than 100 octane number, so you may think of that as well.

anyway , it is all about your philosophy (or no philosphy) in life.