So, this summer I (along with some other members) scored a tremendous amount of oil. I've been hustling it for months. I've got M1, Pennzoil, Quaker state, Valvoline, Carquest, Castrol, Chevron and Havoline. Here are my observations. Marketing works.
* By a 10 to 1 margin, the majority want or demand Mobil1. Even at a higher price.
* Probably 75% demand full synthetics. Folks with older vehicles and on a tight budget will buy the blends. But blends have been challenging to sell or trade.
* Around 10% absolutely refuse to use Pennzoil or Quaker State. These brands simply cannot live down the alleged "sludging" that might have plagued them 30-40 years ago, well before synthetics.
* Advanced Auto was smart to drop their Carquest line. Almost nobody wants it. The full synthetics sells for about the same price as blends in other brands. It was slow to move it.
The takeaway, is that M1 absolutely dominates the oil game from my small experience. I was pretty shocked.
Edit: Out of boredom or curiosity, since I have a fleet of vehicles, I did oil changes in all of them using various brands. I've used QS, Pennz, M1, Chevron, Castrol, and Valvoline. My observation is that the Valvoline, Pennzoil, and Castrol are the best, but there's so many variables I don't think I can really conclude anything. I believe they are all so close that it barely matters as long as you have a premium name brand, and use the correct grade/weight API.