You too can look at www.nfrc.org. It is a non-profit, public/private organization created by the window, door and skylight industry. It is comprised of manufacturers, suppliers, builders, architects and designers, specifiers, code officials, utilities and government agencies. NFRC provides consistent ratings on window, door and skylight products. You should be able to find info. here. Good Luck
I am in the market for new windows also and I was going to go with either Vetter or Simonton Vynal windows. I got a good deal on the Simonton, but I did like the Vetter Windows. They are coming out with a new Wood w/Vynal Cladding that seem to be really nice. The thing I didn't want to do was stain the wood so that is kind of why I went the Simonton wondows, which are very good too. Vetter has been around for 100 years or so, so they must be doing something right.