Low-e windows and double pane windows are both top choices on the market among people who want to reduce heating costs and energy usage. Both windows have their good and bad points.
Double pane windows are the traditional window that slides in channels that are either horizontal or vertical. The panes are separated by a space that is from 1/4 to 3/8 inch apart. This space can be left as is or filled with argon gas for extra insulation and lower heat loss. Most newly installed double pane windows will tip inward for cleaning and can be cleaned with any household cleaner. From the outside or inside of your home they look like clear glass.
Low-E windows are covered in a film-like coating that traps warmth, prevents drafts, and reflects sunlight in the summer to aid in cooling the home. The windows are usually single pane but can be installed double pane at a higher cost per window.
The biggest drawback of Low-E windows is primarily cosmetic. From the outside of the home, the windows may look like mirrors or like they have a blue, oily coating on them. Many people find this cosmetically displeasing in their homes.