1) Do NOT buy your windows from the two big box places.
2) Don't be fooled that "Pella" or "Anderson" is the best game in town. Do some homework.
3) Find a local place window manufacturer who is reputable and find out who they sell to. Then hunt them down and speak to them.
4) The window install itself is easy- its the exterior trim work that can be a nightmare depending what your exterior is (siding, brick, wood) and if you have the tools to do what is needed.
Stupid sister bought six Pellas from Big Blue and two years later wondered the $500 each window had moisture in-between the panels. Pella blamed Big Blue. Big Blue blamed Pella. After I filed the lawsuit for her, and requested discovery on the manufacturing, I found out Pella has a "special line," aka lower quality, for big Blue and Big Orange windows. For once the ridiculous laws in NJ were a positive, as she refused to settle and walked away with $6K, half owed by Pella and half Big Blue, double what she paid!
Her new boyfriend at the time I found a local factory, OKNA who he called about their product. They agreed and we all went on a Saturday. Nice Polish family with a decent operation. They advised who they sell to in our area. My sister did her windows and I jumped on the boat too. I paid $300 flat for every double hung, triple glazed with krypton gas window, installed, despite size. I had vinyl siding and didn't have the machine nor equipment to bend the custom metal flashing and trim. It was well worth it and four years later I am very happy and notice a significant difference.