Ferry ports for France

Yorkshire Swan

I'm hoping to take a week in France late May I have found a site down by Saint Nazaire that I fancy and has vacancies but does anyone have advice regarding the ferry port to use. I will be travelling down from Yorkshire and as its my first time abroad and
still only my first 12 months of owning a caravan its hard to weigh up the benefits of more mileage in France via Dover rather than the trip to Portsmouth and on to Normandy.

Any advice would be appreciated.