We are in the process of replacing our almost 50 yr old, original to the house windows, with Anderson windows. (The glass in our old windows is ok but the wood and screens are showing their age and the "insides", i.e. the lines that hold the squares in place (forget what they're called) are crumbly when you even shut a window, making them drafty; we fixed them all but they're crumbly again, etc. (With new windows this isn't an issue as the grates are either inside or removable and the second "storm window" isn't needed).
The builder we use showed my DH how to install the first one and DH is doing the rest. We've done two so far and still have a bunch to go as money and time allows. They're more energy efficient than the old ones so it should help with heating bills and such.
My in laws hired a local company to put in (cheap) replacement windows and within a few years the seals were broken in most of them and the glass was foggy. Unfortunately the business went under and they were stuck with them with no recourse. Bad for them, but we learned from their experience.
We also know people who built a new house about 15 years ago and just took out a home equity loan to replace the windows, foregoing other improvements they really wanted to make. Not sure what happened there but I gather quality windows weren't used the first time around.
We built a sunroom two years ago and the builder used Harvey windows. I actually like them better than the Andersons (grates are inside, not removable like our Andersons; absolutely gorgeous windows and simple to operate even with one hand) but we'll probably stick with Andersons for the rest of our house since we started with them already. But had we not, we might have gone with Harveys. Either one is good quality. They are not too difficult to put in if you know how.
HTH. Good luck!