JaneSylvia, I'm no window/door expert but my DH and I have some experience. I'm only familiar with Argon gas in Andersen windows. Its heavier than air and has a higher R-value than regular air. Our first dual pane windows were made in 1975 by International (no longer in business). The seals broke on them within 10 years and were so bad you could hardly see through them. Whatever you do, make sure they have at least a 20-yr guarantee against glass failure. You absolutely want LOW-E glass. Having had both regular dual pane and Low-E (Andersen casement) there is no comparison between the two. Plain dual-pane doesn't do much for keeping the heat out in summer. My DH replaced windows and 2 patio doors in a rental house with Jeldwen from Home Depot. Retro is much easier if you're doing the install, but it does reduce the visible glass so it makes your window smaller. Of course, its only as secure as your original frame when the house was built. The Jeldwen from HD are all vinyl and we did have a bad experience with them. My husband accidently hit his boot against the frame of the patio door and a 7" long piece of vinyl broke off. To our amazement the piece was hollow, not solid vinyl. Jeldwen would not replace the door even though it was brand new. Said it was our fault. We think its a design flaw. If you're going to stay in your home and can afford it, I would recommend Andersen. They make a retro window but we've only had experience with their new construction 400 series casement windows and their 12' Frenchwood Glider (it looks like a French door and not a patio door, i.e., 9" bottom wood rail). I also love their screens. They have strong mesh (not the normal fiberglass cloth) and you'll love the way they easily clip in and out for cleaning (we have casement windows). If you want to learn more about dual pane windows, check out my post "Andersen glass failure due to negative pressure". I still think they make a great product! Good luck with your project.

Before you decide on either project, visit one of the recent jobs and make a visual inspection. Yes, retro can look very tacky when they stick a vinyl window inside an alumnimum frame (to save any damage to stucco). You want the most visible light for your dollar. A complete tear always gives you maximum visible light in the opening. Before you buy, inspect! Michael

If that's dry rot I see at the bottom of your frame, its got to go, one way or another. A skilled carpenter (not a "door installer") could cut out the bad bottom section of the stud and replace it with minimal damage to the stucco, but that may be a moot issue. I'm replacing a slider in a stucco wall too and have found that you have to be very lucky to find door with a rough opening size that will just slip into to the old frame without a wide band of trim around the door. That will really be a negative for appearance so we're adding $400 to our budget to cover stucco repair. Most major window mfrs make patio doors in replacement sizes (Integrity does not) and the use of the nailing fin is preferred but optional. If not used, it's bent back out of the way or cut off.

I've not generally been a huge fan of wood/vinyl combo products, but the Aeris is actually fairly compelling, particularly for a wood interior window, prefinished, at a decent price point. I think that you would be happy with that choice... Regarding double vs triple pane, its relative. Is it less important in your area than in a cold climate like here in WI? Certainly. That said, even a triple pane window will only be a fraction of the thermal performance of your walls. If you do a fair amount of conditioning of your interior air (either heating or cooling), you would not be crazy for choosing it at all if budget allows. If otoh you have you windows open 350 days per year, then why bother ;)