The appliance is either Energy Star Certified, or has an EU energy efficiency rating of A++ or A+++. This means it consumes around 20-30% less energy than is required by the minimum local standards for energy efficiency.
Hoover OPH 716DF
The more power per year a device consumes, the less energy efficient it is, making it more costly over time.
Machines which use less water are good for the environment and can save you money in utility bills.
Hotpoint WMFG 8337G
Whirlpool AWE 8840
With a transparent door you can look inside the machine and see what laundry is inside.
A faster spin speed means you can get things cleaner with a lower temperature of water. Using a fast spin also extracts water, meaning that the clothes come out nearly dry. Generally, anything over 1000 rpm is very good.
With a wider range of programs to choose from you can be more specific and choose the best, most economic program for your needs.
With a lower noise level for washing you can worry less about disruption and may be able to do a wash at night or while reading.
More weight capacity helps if you want to wash something heavy like curtains. A traditional household machine can hold around 6kg, so with a machine much bigger you may waste energy using it when only half full.
During a spin, machines can get quite noisy. With less noise the machine is not as distracting and you won't be restricted to using it at certain times.
With a delay start option you can schedule the machine to begin at a later time. You can also set the machine to wash at night if your electricity is cheaper outside of peak times.