I always recommend 120volt. But....
Choose 208volt for dense server racks that need a lot of power. 208volt provides more Uumph per outlet. (U/o) The main disadvantages are that 208volt units are more money and not all computer equipment can run on 208volt .
However, APC disagrees. Their white paper makes an argument for increased efficiency by going to 208volt . While it is true that units draw less current (amps) when you increased voltage (from 120v to 208) and hence cause less heat... its a paltry amount.
I told a customer recently, that I bet him leaving the light on in the server room causes more heat loss than the savings from 208volt to 120v. I suspect I will get an email from someone shortly proving me wrong.
