Summarizing the discussions so far,
it isnt the brand but cheaters representing the brands,
my personal preference ranking for a refill:
a) Total (PARCO)
usually i avoid shell, for the reasons mentioned. E10 in PSO is also rumoured which gave my santro a damaged fuel pump and a tank wash.
The refill scam is true for CNG pumps too, have experienced it twice at the same gas station. the guy filling Rs.20 worth of gas and restarting, his aide (the cashier of the pump) was watching over. I was watching the meter and refused to pay additional Rs.20 to which they agreed seeing my being attentive to their play.
As precaution, always be attentive , get out of the car, and watch closely and do not get distracted.
Also, some pumps have really dodgy digital displays, (small, faded digits, and intentionally dusty panels) watch out for that too...