Talk to someone that understands glazing schedules for your climate. You are doing a bunch of South facing windows, you could consider the passive solar part of the equation if the flooring and thermal mass is available. Irregardless of window or glazing selections, you want an airtight window as a minimum.

Thank you for your reply, Windows on Washington, but I confess you lost me at "glazing schedules"--and Googling left me still unclear on what a glazing schedule is.

"Solar part of the equation" and "flooring and thermal mass is available" are also terms I don't understand.

Glazing schedule is what type of glass is ideal for your climate, build, orientation, home construction, etc.

Based on a large section of South facing windows in a colder climate, you can (with the correct glass type and construction) set up for some "free" energy from the sun when it comes to passive solar heating. You really need someone that understands it and can work with your builder/GC with some of the design aspects.

As a fellow Chicagoan, l will tell you what I have learned. The very first thing you need to decide is whether you want (A) vinyl windows - less expensive than wood, more airtight, low maintenance, but not as nice looking as wood-clad. Best brands are Soft-Lite, Sunrise, Okna. (B) wood-clad windows like Marvin Ultimates. Higher maintenance and will cost $$$. Best brands are Marvin and Kolbe. And no matter what, stay away from Pella (I don't care if your contractor pushes them and tells you "Pella is better now since the class action lawsuit". Nope). Or (C) combo of fiberglass exterior and wood interior like Marvin Integrity Wood Ultrex which have the nice interior wood appearance with low-maintenance fiberglass exterior. Andersen also makes a fiberglass-wood combo (not sure the name). The combos are in the middle in price and appearance bet. all-wood and vinyl. Prettier than vinyl and more expensive than vinyl. Not quite as nice as all-wood-clad and don't have all the extras that Marvin Ultimates have. But they are very nice, beautiful interior, low maintenance exterior.

LoE coatings - in our climate, look for LoE 272. That is enough coating to keep out the sun's UV rays in our latitude, but still let in the "passive solar" heat from the sun in the winter. It's also the standard coating level in most brands' windows, so no upcharge for it. You don't need to go up to LoE 366 in our climate, so don't listen to anyone who says you do. Some people opt for the minimal coating of LoE 180, but you said you have south-facing windows so I'd stick with LoE 272.

Casements vs. double-hung. Casements keep out the wind better and are tighter. Double-hung are a more traditional look.

Double-pane vs. triple-pane. I opted for double-pane though I was strongly pressured into triple-pane. I didn't want to pay the extra for the triple-pane, and for me the double-pane has been fine. You could also do triple-pane on your north-side and double-pane on your south-side. This is an individual decision depending on your budget.

Finally, my one regret is that my windows, which were full replacement, but were not new construction, do not have the same frame depth as the old windows they replaced. That means that hanging blinds inside the frames isn't possible except for the thinnest blinds. My old windows were deep enough to hang anything inside the frames, including thick wood slats. So, when spec'ing your windows, make sure they are deep enough to hang blinds inside. Perhaps one of the experts here could say what to make sure to get in the way of depth.