Double hung versus single hung

Any advice on differences between above assuming double glazed, low E, argon? Brands readily available here: Hurd, PGT, Simonton, Silver Line. Any other brands recommended highly?

As far as air infiltration is concerned, a single hung is theoretically twice as efficient as a double hung. With double hungs, both sashes operate meaning both sashes have the potential to leak air. With single hungs, that possibility is cut in half. You also have less hardware and weatherstripping to go bad. The risk of the window being installed out of square is reduced with a single hung, since the fixed half "should be" square right from the factory. Single hungs are almost fool-proof.... almost.

As far as the glass efficiency, everything would remain the same.

<<As far as air infiltration is concerned, a single hung is theoretically twice as efficient as a double hung. >>

I know i a splitting hairs here, but i think you mean that theoretically air infiltration will be cut by 43%.

Look closely at single hungs. Some manufacturers use a thinner frame and a narrower glass pack in single hungs. A single hung is the "bargain" window of most manufacturers and more cuts are made beside the top sash not tilting in or moving.

harpo is right, the single hung is usually a means of getting the price down. I have some that have a three and a quarter inch masterframe with 7/8" glass and are a nice window. I have others with a two and one half inch masterframes and 5/8" glass packs and are really cheap. The air test are the same on the good ones and a little higher on the cheapies.
For an extra few bucks I'd get the double hungs-so much easier to clean. In as far as the difference in energy effieiency it would be very little.