if this thread goes on long enough about five window manufacturer's reps will chime in

Fiberglass lack the superior air infiltration numbers that higher end vinyl will achieve. The marvin infinity is a pretty good fiberglass window as is InLine fiberglass while the pella impervia is total garbage and cheap looking in my opinion as well as others.

United make what i call " a contractor window". The 4800 is their lower end series and not something we install. Their upper model is the 8000 series which is a mid grade window. Im not fond of the fact that they use a tin plated spacer system and feel the need to utilize fuzzy/ cheat pads in the corners of their windows on the sash. First off, those pads can easily come off and why would they need them in the first place ?? Probably because the window leaks air. Also, on their supposed upper line ( 8000), their locks are plastic which i thought was strange.

the Okna is a much better window and i cant imagine any pro trying to dispute that. If i were ever to use united, it would be the 8000 but again, im still not fond of it.

as far as MI Windows, you are correct. Its a lower end window . Their supposed higher window which they call the 1650 feels weak and they skimp on weather stripping. Most pro's would not use that either.

other good vinyl windows to consider besides okna would be soft lite( imperial or elements), sunrise( vanguard or restoration) vytex (potomac/ fortis), kensington windows.

Okna has been around a long time and is a solid company. Same with most of the others i mentioned.

Thank you for the quick reply. You made our decision easier.

So the classic thing in the glass business is to start a company and sell the hell out of some glass and then go out of business. You should ensure you know how long these names I do not recognize have been in business, and 3rd party verify their claims on numbers. You mentioned some names that I personally have seen stand behind products that were 50 years old.

I agree with a few of the comments above:

1) Defer to performance ratings. These are independently tested and certified. U value, shgc, cr, air infiltration, dp, etc. Get the numbers, but also understand them, because even factual data can be manipulated.

2) On the product, the two mentioned are on opposite ends of the spectrum.

3) Do research on the manufacturer history (length in business, reputation, etc). Just don't forget to do it on the installing dealer as well. A great window is only as good as its installation, and service is only good if the company is still around to provide it.