Gas stations sell gas with different detergents and pumps. More detergents (Chevron's Techron is best) and newer pumps are better.
I used to think there is no difference between different gas stations except price. Turns out I was wrong. There is a difference between both gas brands, or gas companies, and between different stations. Gas stations have gas tanks and pumps. Gas stations buy gas from different companies and place companies' logos on their pumps only if station's equipment complies with companies' requirements. Once I bought gas on a gas station in the middle of Utah, off US-70. The station had a half-scratched-off logo on Texaco on its sign, and a display of different logos on its pumps. The owner explained us she used to buy gas from all these companies, and still buys gas from Texaco, but wouldn't bother with replacing her thirty-year-old pumps to earn Texaco's license. And why should she, if next gas station is eighty miles away. Obviously, old and messy pumps are not good for your car. Choose brand-name gas stations if there is choice.
Different oil companies that sell gas at gas stations start with same oil and same refining process. Before detergents are poured in, gas is a commodity -- not associated with any brand. However, gas contains additives, such as oxigenates and detergents, and these are different from company to company. A bucket of detergent is what makes a taker truck full of gas Chevron, Shell, Exxon, Amoco, or BP. Leaded gasoline was prohibited for highway use in mid-nineties. Oxygenates are used to reduce CO emission, but they also reduce the efficiency of gas, since they contain oxygen that doesn't provide energy. CO emission can be controlled by other means, like catalytic converters, which all modern cars sold in US have. Detergents are added to reduce build-up inside engine. EPA imposes standard minimum detergent concentration, which automakers consider insufficient. Top Tier Detergent Gasoline complies with stricter requirements posed by BMW, General Motors, Honda and Toyota. Chevron, Phyllips 66, Shell and several more exotic gas companies sell Top Tier Detergent Gasoline. Chevron published results showing their detergents significantly reduce engine deposits (build-up), and other gas companies didn't provide similar information. Detroit car makers truck Chevron gas in from Kentucky for EPA mileage testing. I'm in no way affiliated with any gas company and, driving only my own car only as much as I need, I cannot add any personal experience to the above. Chevron gas station is cheapest in my area, and they don't dilute their gasoline with ethanol so far.
I also used to think that higher octane gasoline is better for my car. Turned out wrong as well. Car owner's manual says which gas you should use. There is no benefit to gain from using more expensive grade than your engine needs. Note that octane number (the number that goes with gas grade, usually 87, 89 or 93) is defined at sea level. At high altitudes numbers will be lower.