Actually, there are some differences in gas.
Testing has shown that gas that comes from Esso's refineries (note: not always Esso's pumps, as they sometimes will get gas from other refineries, and vice versa) is the dirtiest, most polluting, gas of the major companies in Canada. I believe Sunoco's was considered the best environmentally because of the 10% ethanol content. Shell and PetroCanada were pretty good because they had invested in new equipment to improve the quality. It was assumed that Esso would eventually do the same but hadn't gotten around to it yet.
I therefore avoid Esso. I use Shell and get AirMiles, or PC and get PetroPoints. Sometimes I use Sunoco and get the CAA points. Mostly, I use the stations that I have to pass on the highway to get anywhere.
And personally, I think gas is too cheap. I'd like to see it hit $1.00/ litre. Maybe then people would drive vehicles with more reasonably sized engines. Who really needs to drive a V8 pick up truck to the office every day? When 4 cylinder engines become the most popular in vehicles, then gas prices will be high enough, in my opinion.