The more appropriate question should be, who do you trust? The car company that was part of a marketing scheme and was paid by the oil companies to promote their gas, or an oil company that refuses to play ball on a marketing scheme...As for Exxon/Mobil, who do you trust? The car company that has no allegiance to a oil company, or an oil company...
Either way, in NJ I have to watch out for dirty gas stations that sell you regular when you choose any grade of gas. I have reported two stations already. My last car I had a hunch, but in this car you notice the difference fast, not just in performance, but I was getting 3MPG less than usual.
Me, I trust neither.
There isn't a "better brand" per say. It all depends on a multitude of factors. Some would argue that one the most important factors is how clean is the underground gas tanks of the individual gas stations.