Perhaps, my memory doesn't go that far back, I was just a small child, probably in the times of Lopez Portillo (aka the dog, "I will protect the peso like a dog", then Mexico had its worst devaluation ever, good job Dog).
I buy pretty well anything that has a pump. I do tend to favor the pay at the pump or full service places. I won't buy gas at Casey's, they've had a few incedents of water in the gas. I think they've taken care of it now, but I still don't trust em.
I usualy use BP as it is somewhat enviromentaly aware and they are usualy the cheaper of all the stations as there are about 50 billion of them. I live near major highways so the prices are a bit more expensive unless I drive further into town.