Hi Doreen, it depends on which area you're in. I would search for windows in google and add your location e.g. buy windows in Ohio
Local contractors usually cling to a brand for the specific homeowner needs of window replacement. What you might consider is bring them in and get a free estimate and base it on quality, warranty, and price. Look to places like Angie List, contractors in your area...go from there. If you choose them to do the replacement, make sure they are licensed and bonded.
Lumberyards usually sell quality windows. A bit different than your local Home Improvement store like Menards though you might check at places like Home Depot, Menards, and Lowes to see what brands they carry. A lumberyard usually sells to contractors doing jobs for customers and they don't carry nearly the amount of merchandise that Menards does. Mostly windows, siding, lumber for decking, trusses, wood framing lumber for homes and outbuildings, fencing, etc. Most lumberyards carry better quality products. Lumberyards do sell to anyone not just contractors. In my area some of the better window brands are Marvin, Anderson, Pella. Just know that you get what you pay for. There are options when looking at windows--even with the better well known quality brands--you can order the least expensive windows, the most expensive windows, or something in between. It just depends on what you want for your home.
Hi Doreen: Call the companies who service your area and get prices and references. Also, check with the Better Business Bureau to see if there are any unresolved issues. Since this is a huge purchase, I'd go with a well known company. Read their guarantee/warranty carefully and see what it does and doesn't cover. Some say that they will charge for the interior wood (between the walls) and some don't. Some say, and I nearly fell off my chair when I read this, that if they deliver the product to you earlier than they plan to install it and it gets stolen, it's on you! And, make sure that the people putting the windows in are bonded and licensed and not 'day workers', or people who line up in the morning to get jobs for the day. You want a company that has it's own workers. See that they cover damage to your house and yard. Finally, check to see if they come to your house to make repairs (one company didn't, and said I would have to take the window to the company for repairs! I'm in Michigan, they are in S. Carolina! And, you can still barter between companies:) I got mine lowered $700! So, there's always that:) Do your homework on this and don't go for the lowest bidder and check those references:) Good luck