It used to be -- probably decades ago -- that when you selected replacement or even new windows for your home, you basically had one choice -- the type of window you wanted (casement, slider, double-hung, picture, etc.). Today things are different; the options and choices available can be mind-boggling.
One of the most important choices you will need to make is the "glass" you select for your windows. You would think that windows would come standard with glass, but that's not normally the case, because there are so many factors involved in selecting the appropriate glass.
How important to you is energy efficiency and lowering your home energy bills to you? Is security a concern where you live? Do your windows need to meet county codes for violent weather? Would you consider decorative glass to give your home a truly beautiful, unique appearance? Do you need obscure glass for privacy? Do you have expensive furnishings and possessions in your rooms that need to be protected from damaging UV light? Will your windows receive direct sunlight or will they be shaded. Would you like windows with glass that practically cleans itself? As you can see, there are many factors involved and we've listed just a few of them here.
Obviously price is another important factor. Triple-insulating (triple-pane) glass made with two premium low-emissivity (Low E) coatings and inert gases between the panes is extremely energy efficient but of course costs more than double-insulating glass made with just two panes of glass, one Low E coating and perhaps no inert gas between the panes. Decorative leaded glass is more expensive than standard annealed glass. Glass made to withstand violent weather costs more than glass that doesn't need to meet such standards.
So, where do you begin? Start by learning more about the choices in glass you have. One source is http://www.gorell.com/pages/high_performance_glass.htm, which provides good information on a number of excellent glass systems. Next research window manufacturers that offer lots of options, not just a few, because your home and situation really is unique. Then meet with a window professional from a reputable home improvement company or window dealer that offers top-quality products. He or she should ask lots of questions to help you decide what you need.
Follow this path, and you will be well on your way to becoming an educated, informed consumer who will be in a position to make the right glass decisions.