We are all looking for lowest cost which is great, but pay attention to turnover. I look for a fuel stop that sells lots of fuel. That way it stays fresh and has less chance of problems.
Kurtee, I have a 2010 Jetta TDI and I filled up at the same QT for the first 4 years I had the car and never had a problem. I also was looking for a place that has high turnover. Then I started getting Check engine lights and it was saying it was a clogged injector. This went on for a couple tanks, but it would clean after some many key cycles. Then one day I need diesel bad and I stopped at a local BP that has diesel. I never got a check engine light with that tank. Next tank was from QT and sure enough, check engine light came on. I have been using only diesel from the one BP station and haven't had a check engine light for over a year. I'm not sure why this started happening, and the BP I go to sells a lot of "car diesel". There are a lot of people that have diesel trucks around this BP.
As far as getting diesel for my tractor, I have 100 gallon transfer tank on a skid that I made for it. BP has driver rewards that takes off of the price per gallon. We have two BP cards and we save up the rewards till I can get diesel for .15 a gallon. You get up to 20 gallons at that price, so I get 40 gallons of diesel at a time. Paying $3.20 for 20 gallons of diesel is pretty nice, plus if I need diesel for my card or truck I can use what I have in the tank since it is taxed diesel.