I personally like Stoners Invisible glass, but have used everything for mega-cheap Tesco-brand 'house' window cleaners before. Some cars seem to have almost a film on the inside of the glass from smoke/vapes/whatever which can make it seem worse when you try and clean it. If thats the case you can use some all purpose cleaner and follow that up with window cleaners, or just apply more window cleaner!
You can seal some windows (polish doesnt really work, and has a habit of making wiper blades skip) but wouldn't recommend it for the front. Works well on side windows and mirrors (if glass, not plastic) and helps keep them streak/waterspot free which helps with visibility. Something like RainX is an option for front windscreens but requires very frequent application and doesn't make much more of a difference than a clean window, Gtechniq have a decent product but its quite expensive and again doesn't last ages.
