I get gas at the Costco in my city only. Any others around us are a madhouse. Our city is only 90,000 people so far and there are 3 other Costco's within 20 miles. That said, if I am driving home, I can glance over from the highway to check the lines. I have kept going because the lines were too long in the past. But they did add an extra pump on each lane and now have the sensors to show you which pumps are available as you pull up, so it has gotten easier/faster.
I do have a friend who swears their gas isn't as good as Chevron or other "Premium" gas stations as he has done the mileage comparisons with a full tank and says he is about 2mpg less with Costco gas.