Casey's or CountryMark locally. BP when I'm traveling. Diesel from truck stops or co-ops (high volume = less water /algae). I've gotten bad gas/diesel from most every other station I've tried.
My wife and I actually do mileage tests when we get a new vehicle. We'll fill it up at different stations and see which one gives us the best mileage and least problems. Her Saturn in very sensitive to ethanol (hard starts, misses, and terrible mileage). Every time she puts gas in from Sams Club, I get to hear her complain about it for two weeks
I get my diesel from Murphys, its usually a couple of cents cheaper, it's American and I've never gotten a bad tank.
On the road I always buy at truck stops where they do a good volume of business as 6 birds said less water and algae.
Flying J or Mr. Fuel for diesel for the same reason as mentioned above. Gas for the wifes vehicle is purchased from whoever has it cheapest, which right now is Kroger (due to the loyalty card disc. when we buy groceries.)
I always buy from Shell. I have used "cheaper" gas (i.e. Speedway), and the car ran awful. I guess I am a sucker, but that is my experience. I feel its worth it to pay the extra 2 cents per gallon.
I try to stay away from the gas stations where you put gas in a gas can in the winter, and the next day when it is only 15 degrees or so you have a chunk of ice rattling in the can lol. Try to buy mostly at co-op ( country mark, energy 24)
As I understand it, most major brands in the Indianapolis area all get their gasoline from the same place: the Rock Island terminal up at 96th & Zionsville. That being said, the East side of Indy (on Shadeland) generally has cheaper gas than the NW side of Indy. The Flying J at Fairland Rd on I-74 usually runs somewhere in between the two of those. I try to buy gas from whomever is cheaper - and on my way.
speedway gas in every car i have owened ran like junk. prem. in my bmw's thru the lights/codes. oddly enough i could run Meijers Mid grade in both of my bmw's with no problems at all.
i prefer meijers or swifty. usually run marathon though because its more convient... shell if in a pinch... bp all out last resort. (more of the oil spill then anything, they used to be my number 2 pick)
Kroger or Marathon. Or wherever I can make it to. I tend to run the gas low sometimes, only ran out once and that was due to a bad fuel sending unit, haven't run out since.
I usually go for the cheapest chain. i don't particularly trust the little mom+pop places cuz I got a tank from one of them that had to have been cut with a ton of ethanol. I usually get ~420 miles to a tank, and I got less than 360 on this gas. the national chains don't want to risk their reputation by cutting it with more than 15% (legal limit before its an "alternative fuel") and I've not had bad experiences with national chains.
any station with a sticker on the pump that says "this gas may contain up to 15% ethanol" gets a pass.