There's only one 'paint' for exterior hardwood – Sovereign SX70 – stain and clear top coat. I guarantee you will not be disappointed (except possibly by the price – but quality comes at a cost!). I have used it on my front door and everyone that comes to the house comments on the gloss and durability of it.
Sovereign Chemicals are based in Barrow in Furness, Cumbria (tel 01229 870800)
For paint I would recommend Sikkens 'Rubbol AZ Plus' it is what they use on the front door of a particular house in Downing Street, London! Available in other colours than Black though.