A gas boiler may be cheaper to operate. A gas boiler will not stop working if the electricity goes out. An electric boiler is less likely to generate the risk of a gas leak, and is cheaper if gas prices go up.
A gas boiler recovers faster so that makes it more efficient but it is more expensive than the electric boiler the difference in the two recovery times is significant the gas boiler is probably 50 to 60 percent more efficient in recovery time that the electric boiler would be for you.