Replacement window? I am looking to purchase 7 replacement windows before winter. What brands...

I am looking to purchase 7 replacement windows before winter.
What brands are suitable?
I want something that will be very energery efficent, any suggestions as to what I should look for?
Idea on cost per window? All 7 are impossible to tell apart size. Where should I shop, lowes, homedepot, elsewhere/
Answers:    At home depot and lowe's, you need to be careful not to buy the lowest price window. Do you want wood, aluminum, vinyl-clad wood inside, vinyl outside? All that will hep determine the price. I would try to contact some contractors and get prices. We bought Harvey and are very pleased, but I am sure there are others out there. You want low-E, double pane. You can do comparisons online and find out what things to look for. If you jump to the brands that send you flyers, some of them are a huge rip off. I suggest our windows were between $200-$300 per windowpane. They have panes inside the chalice, they tip out for easy cleaning and we are quite pleased near them. You could go for major brand approaching Sierra Pacific, Jeld-Wen, Pella, Marvin, but then you may be in another price point. In our contemporary house we went with SP, but they are wood window and have more bells and whistles. Shop lots earlier making a decision. Good luck