When you are comparing windows, these are the four big factors you need to consider:
1.VT=visible transmittance. This is how "light or dark" the window appears. Each coating or pane of glass lowers this number. The higher the closer to clear it is, the lower the number, the more it looks"tinted".
2.Whole Frame U or R value. You want to find whole frame values, because center of glass measurements completely ignore the frame and whether it is insulated or not. Also, U=1/R or R=1/U will let you compare apples to apples. I prefer to view all windows as R values, because I am used to seeing things that way. STAY AWAY from any "equivalent" numbers. This is where people try to make their product look better by trying to combine air sealing or thermal heat gain into one number. None of those parameters have the same units as R or U, and should be viewed as separate parameters.
3.Air Sealing= How well does it stop air from blowing into/out of your home.
4.SHGC=Solar Heat gain coefficent. How much heat in the form of light does the window let in. Higher is better on south facing windows with adequately sized overhangs, and lower is better everywhere else.
Are they worth the extra money? To technically solve this, you need to do a heat loss calculation, by finding how many square foot of windows you have, then for each type of window (such as double pane vs triple pane) using how many heating degree days and cooling degree days, you can calculate how many BTU's a year you will lose through each type of window. Subtract the better windows number from the worse windows number, and you can determine how much energy you will save in a year. Then, with your specific heating or cooling system, you can determine how much money that is worth, and from there base you purchasing decision.
Want the short answer? Unless your house is already very well insulated (R30+ walls, R50+ attic), or you have many large windows (economies of scale make larger windows more affordable per square foot), or you value your carbon footprint as worth more than your money it probably isn't worth the extra money over a good quality double pane. (I consider good quality double pane to be Low E, argon fill, and insulated frame.) That being said, the last house I worked on we found some vinyl triple pane windows from a local manufacturer for barely more than the cost of double panes.
All that being said, I will answer your question about who makes the best triple panes. I know I am about to open up a can of worms (some people on here like certain brands and tend to ignore any evidence that another window could be better), but comparing advertised numbers on data sheets, Serious Materials makes the best insulated windows out there, if you want to pay for them. (I am not affiliated with them in any way, I have just done my research.) Their Fiberglass 725 series is a "triple pane", with two glass panels and a suspended thin film, which acts like a pane of glass in preventing air convection, but is actually clearer than glass to let more of the visible spectrum in. If you are on a tighter budget, Serious also makes a vinyl series of windows, but with lower whole frame values. It is definitely worth your time to call them up and get a quote.
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