Hi
It really depends on the amount of grass you need to mow. If you only have a small amount to do then maybe you would be best off with an electric mower, such as this one here:
https://www.diydoctor.org.uk/DIY-superst ... -volt.htmlIf you have a fair size lawn that involves quite a bit of mowing then you would certainly be better off with a petrol mower (cuts better and also no wires to worry about). In terms of efficiency, most small engine petrol mowers are much of a muchness. In general, the more horsepower they have the more fuel they will use (depending on how hard you rev them and how much work they have to do), but on the flip side of this the smaller the engine and less horsepower it has, the harder you will have to rev them to do the work so the more fuel they will use, if you see what I mean.
In terms of quality and reliability - In general, the Honda mowers tend to be some of the best and most reliable.
Hope this helps