P21S wax is very good. As for a product you must have, I would say that any product which really helps in the prep of your paint is worth while. P21S, Zanio, Pinnacle Souveran Wax, none will look great if the prep is poor.
Whilst I would strongly disagree with your comments on Autoglym, I can highly recommend Alex as a good guy to buy from. If the swirls are minor it might be worth looking at Clearkotes VM. Some love it and some dont, I like it and it is very easy to use