Generally 220v anything works easier or with less effort so can be cheaper to run. Appliances that run off 240V draw less current than 120V appliances so lighter wiring and fixtures can be used. However, 240V is more prone to arcing than 120V. Also, 240V is more likely to blow you away than 120V, whereas 120V is more likely to "grab" (Cause your muscles to involuntarily contract, i.e. making your hand grab a conductor) you. Also the US uses 120V because Edison originally used 100V. It was upped over the years to cope with demand. The US also has 240V in residential service for large appliances like ovens and dryers.