I hired HD to do the three bay replacement windows in my bedroom. I
watched them work and asked questions, which they were happy to answer
-- to their credit. I then went ahead and replaced the other dozen
windows in my house myself. I did a much better job than they did
insulating the cavities where the weights used to be. I also used more
care to not scar the molding with my pry-bar.

A contractor will never care for your positions or your heating bills
like you will. If you're at all handy, replacement windows are not
hard. Full window replacements on the other hand could be a little
tougher.