If you cars are quite new (under 6-months old), the recommendation is not to polish them as the paint is still soft. Even after that stage, it is worth buying a wax/polish that allows the paint to breathe; otherwise you can get into trouble with vapors being trapped by the wax layer.
I've found Alex who runs
Serious Performance car care products to be great for advice. His prices are also excellent and often has things on offer that he can recommend.
