In my experience, windows will always have some sort of film on them unless they are stripped-off completely of any grease on their surface. Window streaks are probably one of the most stubborn problems to fix in car detailing. This means that windows will look best without PROTECTION. First of all, clay bar the area. Please see my thread "How to detail a crossfire" for more info. Then, get an automotive wax and grease remover (I use Crossfire...no joke, that's the name) from any autoparts store and apply it to the windows straight with a quality microfiber towel. Reapply multiple times in small sections until streaks disappear, using more than one towel. PLEASE make sure you wipe the wax and grease remover immediately after application (within 3 seconds). Your windows should be streak-free. But, I'm not sure if this is the best way to go. Your window will be stripped off of any protection. So, the second best thing to do in my opinion is, after the windows have been stripped and streakless, apply a paint cleaner (thinly) and then a wax (thinly) to the area to provide protection from the elements and to allow water to fly off at highway speeds (no wiper blades).