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if safety during using electricity appliences is excluded, higher voltage lines are better than lower ones . i mean power supply of 230V is better than 120V. here is the reason:
from wikkipedia:
Electrical power is always partially lost by transmission. This applies to short distances such as between components on a printed circuit board as well as to cross country high voltage lines. The major component of power loss is due to ohmic losses in the conductors and is equal to the product of the square of the current and the resistance of the wire:
For a system which delivers a power, P, at unity power factor at a particular voltage, V, the current flowing through the cables is given by 
. Thus, the power lost in the lines, 
Therefore, the power lost is proportional to the resistance and inversely proportional to the square of the voltage. A higher transmission voltage reduces the current and thus the power lost during transmission.
In addition, a low resistance is desirable in the cable. While copper cable could be used, aluminium alloy is preferred due to its much better conductivity to weight ratio making it lighter to support, as well as its lower cost. The aluminium is normally mechanically supported on a steel core.
link: http://en.wikipedia.org/wiki/Electric_power_transmission