Twenty five years ago one in 100 customers would ask about the windows included in the package. The answer was "all wood, double hung, double glazed." End of discussion. Today 50 out of 100 customers will ask about the windows and their interest is in energy efficiency and maintenance. Although the choices are many, the bottom line is windows are not very energy efficient. Our recommendation to our customers is to get a good quality moderate cost clad, double hung, double glazed, low E window. Our experience tells us maintenance will be more important over a long period than the energy costs associated with a good quality window. The high cost for a slight increase in R value isn't justified. Look for low maintenance features instead. The specific choice should be kept in line with the overall budget for the home. There are many brands in this category such as Jeld-Wenn, Pella, Hurd, Weathershield, and many more. Put that extra money into more effective energy saving areas such as higher rated furnaces, extra ceiling and wall insulation, and energy efficient water heaters and appliances.