I've had fiberglass windows from Pella installed for about 7 years now, and honestly, they've held up really well. We get some pretty extreme temperature swings here—hot summers, freezing winters—and I've noticed zero issues with warping or seal problems so far. I do agree installation is key though; my neighbor went with a cheaper contractor, and he's had nothing but headaches with drafts and condensation.
On the environmental side, I hadn't really considered that when I bought mine, but it's good to know fiberglass is a bit greener. Personally, I chose fiberglass mainly because of the thermal expansion factor you mentioned. Vinyl windows have definitely improved, but I figured if I'm investing in something that'll last decades, I'd rather spend a bit more upfront and not worry about it later.
Still, if budget is tight, quality vinyl windows installed right can be a solid choice. It's really about figuring out your priorities and how long you plan to stay in your home.
I've installed plenty of fiberglass windows from Pella over the years, and yeah, they're generally solid performers. But honestly, I've seen a few cases where even good fiberglass windows had issues—usually because of sloppy installs or cutting corners on flashing and sealing. You're right about installation being key...a great window poorly installed is just an expensive headache. Fiberglass is definitely less prone to expansion issues than vinyl, but if budget's tight, quality vinyl with proper install can still do the trick. Just don't cheap out on the contractor.
I've also worked with Pella fiberglass windows, and your point about installation is spot on. I'd add that proper shimming and ensuring the frame stays square during install can save a lot of headaches down the line...seen plenty of DIY jobs go sideways because of rushed measurements.
Totally agree on the shimming—it's one of those little details that seems minor until you're staring at a crooked window frame wondering where it all went wrong, haha. I've installed a few Pella fiberglass windows myself, and honestly, they're solid windows if you take your time. But I've also seen folks rush through measuring and end up with gaps big enough to let in a small bird. Measure twice, shim carefully, and you'll probably be happy with them.