We posted on this one over a year ago and said we would never do the Portsmouth - Santander trip again!
However, 18 months of reflection and we are ready for another go. We went over in February 2008. Unfortunately our trip coincided with one of the worst storms the crew could remember. We were due to board at 21.00, but bad weather delayed the incoming ship and we boarded at 04.00. We went straight to bed and in spite (or because of) the rough weather I would have slept soundly if it were not for my wife screaming out out every time a large wave crashed into the side of the ship. As soon as we reached the Bay of Biscay, the waves were head - on and the ship more stable, so the rest of the trip was not too bad.
Instead of reaching Bilbao at 08.00 we didn't get off until 14.00. We didn't want to stop as the car was loaded with very stealable stuff, so we decided to plod on. Luckily I had just been given a Tomtom satnav by the kids and apart from a poor start caused by my fumbling the instructions, once we got on to the motorways everything was fine. I needed fuel, so we has a short stop for that and stopped again for a quick 'lunch' somewhere north of Madrid. Madrid came and went in the dark, but faithful Tomtom kept me on the straight and narrow and we reached Formentera at about 23.30, so the trip, including breaks took us about 91/2 hours, much of it in the dark, without ever exceeding the speed limits.
After 2 months we did the return trip, this time starting at about 13.00 and driving until dusk, finding a hotel and driving the last 120km the next morning. Again the ship was a bit late, but not excessively and although the weather in the Channel was again poor, docked only a little late. Altogether a far nicer trip.
The thing to remember is that it's just a ferry! They sell it as a mini-cruise, but it's just a glorified channel hop and the facilities are pretty basic. I spent most of my time sitting in one of the lounges reading, taking the occasional 'constitutional' walk around the ship, going up and down the various decks by the stairs to get a bit of exercise, but unless you are into smoky 'night club' bars, there is little else to do. There is a cinema, but of course if the weather is rough a hot, windowless space, is not the place to be and its expensive, as along with all your food and drinks, it is of course extra. I dubbed them the Ryanair of the waves as they seem to charge you extra for everything you wanted, which after paying almost £600 for the trip, seemed unreasonable. On a real cruise an all inclusive price for a luxury trip is about £90 per person per night, this works out at about £110 pp/pn on the same basis.
That having been said, we live in Canterbury, 12 miles from Dover / Folkestone and could easily take one of the shorter hops to France and motor down. We have yet to try this because we take as much as we can in the car and after friends had had their car burgled at an overnight stop, we feel that we would rather not risk it. We could go over via one route and back another and we might try that sometime. If you live somewhere near Portsmouth, (about 120 miles from us) I would have thought the Bilboao or Sanander crossing was a no-brainer, why add over 100 miles each way to your trip to travel via the Kent ports, but then, what do I know? The traveller facilities in Portsmouth are pretty dire if you have any delay, but they are heaven compared with those at Bilbao, so don't aim to stay long in either.
I can't remember how much we paid in Spanish tolls, but it was insignificant. We have since used the Michelin web site to gauge the cost of both routes and the differencee is very small once tolls, fuel and overnight stops are taken into account. We also save on this years horrendous car hire rates by using our own vehicle. I don't personally find driving a RH drive car is a problem. Most of the trip is on dual carriage way, where you simply look in the other wing mirror and if you are using single carriageway roads, time is clearly not of the essence, so overtaking not a priority. You are also more familiar with your own vehicle and need to give far less concentration to operating an unfamiliar, over used and under maintained hire car.
Well, I hope this is of some help (it's the longest post I have ever made), whatever you chose will clearly be a matter of personal preference, but having made your choice, I hope you enjoy the trip.