For a widely varying climate like we have in Ontario, there is no better window than a fiberglass window. Fibertec was on our list of companies to call from the start, just based on their reputation in the industry (recommended by our architect).
The good folks at Fibertec (we mostly dealt with Steven Hall) definitely lived up to our high expectations and more. They were cheerful and interested in learning about exactly what was important to us in our home. (e.g., light, air flow, etc.) And they were just as eager to talk us out of bad decisions to help us keep our costs under control. (Not sure how many companies would do that!)
Steven was always helpful and not the least bit pushy. His quote was put together professionally and was very easy to understand.
We wound up going with one of their highest end products: triple glazed, krypton filled and with a u-value (insulation rating) so low, the windows will lose less heat that the WALLS of our old house did. (It's a good investment though: the math says the extra costs pays for itself over the life of the windows -- we're paying more on our mortgage but less on our energy bill. And the house will be a much more comfortable space to live in, too!)
The windows showed up bang-on time and our builder had no trouble getting them installed for us. (Well... there was a comment about them being "the heaviest window he's ever moved" but it was said at least partly in admiration of the triple glaze. The other part was definitely just that some of the larger windows were REALLY heavy. :-) )
And they followed up to make sure all was well with their product after installation. It was a really good experience through and through.