Low E/argon filled, three pane.

Speaking as one who installs a lot of replacement windows, I would suggest that you open your Yellow Pages, find a number of installation contractors and ask them which manufacturers are the best. Don’t ask just one ow two people – you need a broad cross section. There is probably a regional company that makes really great windows at a reasonable cost, but you’ll need to find them (here in New England, it is Harvey). After you talk with a bunch of contractors, one name will come up repeatedly and that’s who you want.

I’m a very big fan of Pella for the money. Double hung welded vinyl. Anderson windows are probably the most expensive on the market, but don’t let the price indicate they are the best. As far as performance, they are no better than Pella.