It also comes down to the price one pays for electricity.
The Antminer S1 cannot be beat if one has low electricity costs (under 10 cents / KWh) and has access to abundant electricity and cooling.
I may pay less per GH for electricity in dollar terms running S1s at 10 cents per kilowatt hour than someone in Europe or California pays to run SP10s at 30 to 40 cents per kilowatt hour.
Power efficiency is very important for miners with high electricity costs, but not so much for miners with low electricity costs.
Certainly true to a point, but too much is made of relatively small power efficiency differences. The more you pay for the gear up front, the longer it has to run to reach positive ROI and state of the art efficiency generally commands a premium. People with really high power costs can have their sha miners turn into losers very quickly even with state of the art efficiency. If you're in Australia for instance and paying $.34/kwh then pre-ordering an sp-30 for August delivery with btc/fiat under $500 and difficulty continuing to ramp up is a huge risk. In such a case you should buy and hold coins, but if you're determined to mine then scrypt gear is probably a better investment than sha gear anyway. The calculations are probably more crucial for people on the margins of high power costs.
@Mc Trollster. You win the most annoying post of the month award sir. It hurts my eyes to look at your dumb picture. Ignored.