Most garages carry 'Premium' fuels which promise better fuel economy. Without doubt, they generally provide additional mileage per gallon, but it's not necessarily saving you money.
If your vehicle will run on the standard, it's often cheaper per mile, even if your MPG appears to be worse. So do the maths, calculate the mileage you get per gallon and then divide by the cost to see which works best for you.
Similarly, try fuel from different Garages and find which works best with your vehicle.
Note: You should, however, try both types for around a month each. You'll unconsciously change your driving behaviour each time you change fuel, which will skew your figures if you don't allow time for things to normalise.