120 V 230 Volts mains, which is best?

[ppppenguin]

With modern electronics you could now make a case for DC distribution. Many appliances (kettles, toasters, irons etc) wouldn't care and anything with a switchmode PSU would be simpler if it was DC only. Localised microgeneration (PV, wind, battery banks in cars and homes etc) would probably simpler too. There would be a huge amount of power electronics in the distribution network but HVDC uses long distance links more efficiently. Partly because peak voltage = RMS so a circuit with given insulation could utilise a higher voltage than with AC.

Switches would be harder. Modern microbreak switches are not OK for DC at 200+ volts.