You're in RI, right?
I just replaced a bunch of windows with Andersen 400 series new construction windows. These are their top of the line double hung window, wood interior, etc. There are windows that are probably better and there are windows that are definitely cheaper but lots of contractors prefer to use them.
MW is a Virginia company, not real well known in New England, but if your contractor likes working with them, that is a plus. The MW 800 is a vinyl clad wood window, the Silver Line 3000 is an all vinyl window. What look are you going for?
SilverLine was purchased by Andersen a few years ago. They recently closed their manufactuering plant in Mass. due to the economy.
If you're just going with a vinyl window for the sunroom, I would probably go with Harvey. They're local and well supported in New England.
http://www.harveywindows.com/