Which gasoline brands are better? and does anyone know which one Audi recommends?

According to this report there is an difference in gas.

Yes. The above specifications are intended to ensure minimal quality
standards are maintained, however as well as the fuel hydrocarbons, the
manufacturers add their own special ingredients to provide additional
benefits. A quality gasoline additive package would include:-
* octane-enhancing additives ( improve octane ratings )
* anti-oxidants ( inhibit gum formation, improve stability )
* metal deactivators ( inhibit gum formation, improve stability )
* deposit modifiers ( reduce deposits, spark-plug fouling and
preignition )
* surfactants ( prevent icing, improve vaporisation, inhibit deposits,
reduce NOx emissions )
* freezing point depressants ( prevent icing )
* corrosion inhibitors ( prevent gasoline corroding storage tanks )
* dyes ( product colour for safety or regulatory purposes ).

http://faqs.cs.uu.nl/na-dir/autos/gasoline-faq/part2.html

but the question is which Brands are better