With utility bills constantly rising and due to continue this escalation, due to the clean air act and the need to buildout the energy grid, the best thing you can do is make your home as energy efficient as possible. One way to do this is to go to the configuration that is the most energy efficient. Casements, picture windows and awnings are the most energy efficiently designed windows readily available in the US. One of the BIG reasons they are more energy efficient on the casement and awnings, is that when the wind blows, it actually blows the sash TIGHTER against the frame forming an even better seal, wheras on tilt in windows the wind blows the sash away from the frame and leaves more chance for air blowing around the sash between the sash and frame. ANOTHER way to make your house more energy efficient is to look at triple glazing options. There are many configurations, including argon gas and krypton gas and mixtures of the two. These configurations have much better U values (Rfactors) than even the much better dual glazed options that are presently commonly used. The case for picture windows should be fairly obvious, in that there are no operating sashes to allow much air to penetrate.