I use DP Krystal Vision & a microfibre window cloth, well, a damp one and a buffing one.
Best to do it in bright sunshine, so it flashes off quicker & you can see the smears you've just made & repeat the process.
I believe it's the VOCs from the heater ducting that cause that grey film - new Hondas are terrible for it, but the effect decreases as they age. Of course, a hot engine causes it too, on the engine bay side of things.
The trick seems to be to hit it regularly. Once it builds up, you just move it around.
Nick
“I find myself irresistibly attracted to cars that nobody else buys. The NSX is a classic of the genre because nobody buys it and yet it’s a fantastic car. It’s got a wonderful compactness and simplicity and unpretentiousness to it. Honda rudely continues to make them whether we like it or not, even though there can be no commercial logic in doing so — I thoroughly admire that.” Rowan Atkinson