Did our whole house 4 years ago. Went with vinyl clad replacements, and has been mentioned, replaced the entire window, and while I was having it done, had the exterior wood around the windows wrapped in vinyl as well. Now they are entirely maintenance free.
Went with a low e double paned glass filled with argon, I believe, and make sure you get the type that tilt in, makes cleaning them a whole lot easier. Wasn't a cheap remodel, but our electric consumption has dropped appreciably (electric heat pumps up/down for heating/cooling). Due to rising electricity prices, the bills haven't dropped all that much, but our kw hour usage is way lower with the new windows.
It's been awhile since I did the research, but I figured the payback would take 7-8 years, or so, back when I was looking into them.
Many good brands out there from which to choose, key is in the installation, as I think once you get to a certain level, there's not all that much difference between the major manufactures.
Good luck! Must admit, I don't miss seeing the curtains move when the wind's blowing!