We went with the best I could find - fiberglass triple pane from Fibertec in Canada. http://www.fibertec.com/

 I designed our house so almost half the window area faces south to take advantage of passive solar. And we special-ordered the south windows to be NOT low-e so they would let the sun warm the house on winter days. (In the summer we have large enough eve overhang that the south windows are shaded. The outside temp can be in single digits and on a sunny day the furnace won't run all day due to passive solar heat. It's the best bargain you can get.