There are many many different kinds of replacement windows. We use only lifetime warrantied fusion welded vinyl windows. All of our windows come standard with low-E  insulated glass that is argon filled. We provide our customers with custom-made windows from 4 different manufacturers. These manufacturers are Alside, Simonton, Custom Window Systems and PGT. Each one of these manufacturers has something that they build better than the others. We use Alside for about 95% of our residential replacement jobs. Below I've listed the four manufacturers and a link to their web site.