My uncle is self-employed, and as been a window/door installer for 40+ years. I worked with him full-time for 3 years, so I had my fair share of window/door installs, so here's my advice, it's free so it certainly can't hurt...
We only worked with Andersen and Marvin, and there's a darn good reason why. As with any product, there are the bottom of the barrel (Jeld-Wen, Gilkey, Champion, etc. etc.), mid-grade (Pella), and high end (Andersen/Marvin). This is of course excluding custom manufactures, and is subject to local availability. There may be other REALLY good high end manufactures in the US, but the cost was too high for "normal" people or just were not available through our distributor.
Within each product, there are different models and options, just like vehicles. Andersen for example, starts with the vinyl-clad 100 series and goes up to the 400 series Woodwrights. The 100 series are a great cost-savings window, if the vinyl-clad look fits your style of house. Obviously they are not going to be built to the same standards as a 400.
With windows/doors, you need to think about insulation values and durability. While an "expensive" window/door may costs more upfront, if they last 2-3+ times as long, is it really a bad investment?
Personal experience:
Marvin are the best, simply put. They are extremely expensive however, and surely out of most peoples price-range.
I would recommend the Andersen 100's if you want a cost-effective vinyl-clad, the 200's if you want more of a wood-look window, and the 400's if you can swing it. The 400's are really good windows and are what we installed ~80% of the time.
By far the most important thing is to get a good contractor that actually knows what they are doing! Simply taking out an old window and screwing a new one in absolutely not how it works. It's certainly not rocket science, but there actually is a lot of knowledge that goes into proper installation to make them last a long time and not rot out frames, have condensation, sticky (hard) open/close, etc. Go to your local lumbar yard (NOT HD/Lowes), who actually sells Andersen windows (and not Renewal by Andersen - totally different), and ask them for a recommended contractor.
My uncle uses 400's in his own house, and I'm currently building a house using the 400's. You should absolutely expect to spend ~$300-500 per window (depending on size) and a labor fee of $500/day was my uncle's rate plus material costs (trim, caulk, shims, etc.). Jobs were bid by the number of days to come to a final price, 8 windows would probably be ~$8,000-10,000. To give you an idea of just window cost, my house is using 21 various size 400's and an 8' 400 slider, pricing is ~$13,000. This obviously doesn't include the other materials listed above, or labor. This is for double-hung, casements costs more, and depends on options.
