If you have a choice, do not install replacement windows. I know each manufacturer claims that their window is the greatest window ever made. They are not going to last and you will encounter problems after a few years. Even though the initial cost is high, stick with a quality brand window that will last for twenty years and more. I have used Anderson and Pella windows for years and have never had any complaints. No matter what the choice try to avoid using any type of sliding window.