The gas boiler is typically cheaper to the oil boiler, but they do not tend to last as long, the oil boiler needs more servicing as to the gas, as the jets wear and so the pressures need adjusting more often. Also, the gas boiler tends to be able to modulate more than an oil boiler, so can better match the output required, and if not modulating type, the on/off/on time with gas is shorter to oil, so higher hysteresis with oil. You also need an oil tank, and a bond around the oil tank, and you need to order the oil in advance, where with gas not need to look to see how much you have left.
So not all down to price of oil fuel or gas, I did have gas, I now have oil, and the oil is cheaper even with a larger house, but if I had the option of town gas I would go with town gas, but would not go with LPG as that is basic a bomb in ones back garden.