I use Turtle Wax ClearVue Rain Repellent all year round (re-apply every 2 months) on the windshield. Never seen fog or smearing, but maybe that's due to how i put it on:
1) thoroughly clean the window (+ clay, cleanser polish)
2) 3 times up-side-down the bottle to load a big make-up pad for use half the windshield, wipe until it dries. Repeat for other half.
3) wait 30-60 minutes
4) Repeat 2) and 3)
5) Wipe the windshield crystal clear with a non-woven microfibre glass cloth and some sprays demi-water.
For rear- and side windows i use the same sealant as on the paint and wheels — FK1000P.
But this all doesn't prevent ice not freezing on the windows, it's just easier to remove and then leaves a crystal clear view. When it's freezing or snowing i just use a windshield cover and de-ice the other windows with plain cold water.