One of several installation methods may be more appropriate for your situation than another. There is always a cost trade-off so you need to know exactly how a contractor plans to approach your job and why a particular installation method is being used. Factors that determine which installation method is to be used include the frame construction of window that is being removed, the frame construction of the new window being installed, and the personal preference of the owner.
WARRANTIES

There are 2 separate warranties for a window installation!

"Product warranty"
from the manufacturer
These warranties vary. "Life-time" does not always mean material and labor on all components of the window.
Warranties vary by manufacturer on extrusion, glass failure, glass breakage, mechanics, and screens.
Whatever is important to you, be sure to ask for a written guarantee.
"Installation warranty"
from the contractor
This is a guarantee against leakage due to a faulty installation, material and/or procedure. This warranty is only as good as the company, or person that installed it. Consider what is the likelihood of the contractor being in business…? A "lifetime” installation warranty from a company that doesn’t have the financial backing of a very large corporation such as Home Depot, may not be worth very much. A-TaylorMade Window provides a written 10-year written warranty which provides a length of time to identify any deficiencies in the installation.