which brand of car fuel is the best in quality?

Each major oil company typically adds its own proprietary additives to the basic recipe for gasoline in order to provide or enhance specific performance features. And, most important, each company provides the technical expertise to back its brand. They also ensure that the additive package is contained in every gallon of gasoline sold under their brand name. Many customers buy branded gasoline because of this consistent quality. Deposit control additives, which are found in all gasoline by law, keep engines clean and make them run more efficiently.
So all the gas are same, the only different is additives(添加劑). It really depend on the customer what they like and which they believed is the best. Of course, all the oil companies said the gasoline are the best, but to me they all about the same, the only different is the octane, the higher octane is better for the vehicle, it has less deposit for the engine. The lower octane gas causes knocking in the engine. Knocking can damage an engine, so it is not something you want to have happening.
Hope this can help you with!

I would suggest SHELL. It has good quality petroleum.