GTechniq C4 gets my vote
GTechniq C4 - Awesome stuff, needs to be put onto clean degreased surface but it awesome
Dodo Juice Supernatural- It's lasted +12months on my mirror caps but it's difficult to apply because it takes time to cure.
BlackWow- Good stuff on smooth and certain plastics but in my experience didn't last on clios mirror bases/scuttle pannel/fog surrounds etc.
Auto Glym- Great stuff if treated like a wax (put on, leave then buff excess completly off with mf) Doesn't last as long as the 3 above though imo.