Auto vs trains: Barcelona, San Sebastian, Bilbao, Madrid

San Sebastian/Donostia to Bilbao/Bilbo is only a bit over an hour by coach. By rail it takes quite a bit longer and the local trains up there are pretty clanky. I'd only hire a car to do this if you planned to make a day of it and travel inland to visit other places along the way. There is a lot worth seeing in the region. If you you just want to move from city to city then take the coach (bus).

Admitedly, I don't know anything about Barcelona to "S/Seb" but I imagine it's a long journey and probably involves a change or two if going by railway. Have you considered flying to Bilboa airport from Barcelona instead? Otherwise I'd drive but stop off for a night along the way.

The AVE high speed train is still undergoing construction in the north of Spain and is not so well connected as it is in the south of the country. There is currently no direct train connection between Barcelona and San Sebastian/Bilbao (it's actually quite convoluted), one has to go via Madrid instead.

If you would like to stick to public transport, you could train from Barcelona to Madrid, then from Madrid to Bilbao, and then train from Bilbao to San Sebastian. Personally, I don't think the majority of this route is very scenic and I feel the north is best experienced with a car, which allows you to stop at the more off the beaten path sites like the Poblet Monastery, Loarre Castle, and the Olite Royal Palace.

I am not sure how many nights you have available, but with a car, I would do a mini road trip along these lines (note there is a lot more to see and do in between Barcelona and San Sebastian than what is listed):

-Start Barcelona - (5 nights)

-Poblet Monastery - a UNESCO World Heritage Site, a still active 12th-century Cistercian monastery located in western Catalonia - one of the largest in Spain. It was a fortified medieval royal residence and now contains the unique hanging tombs of the Kings of Aragon.

-Zaragoza (2 nights) - Capital of the Aragon region. More than 2,000 years of history including Roman ruins of the city walls and amphitheater and the Aljafería, an 11th-century Moorish palace. It also has the famous pilgrimage site of Nuestra Señora del Pilar basilica, housing the miraculous image of the Virgin Mary.

-Royal Palace of Olite (1 night optional) - For me, one of the most impressive medieval castles in Europe. The seat of the Kings of Navarre. There is a also pretty good Parador hotel next door.

-San Sebastián (3 nights)

-Bilbao (2 nights) Drop off car here, take train south to Madrid

-Madrid (4 nights) Fly out of Madrid

These are rough estimations of how many nights I feel is needed to see the immediate city with no day trips. Hope this helps :)

I'd start by comparing travel times. Use ViaMichelin.com for driving times, but recognize that they make no allowance for stopping, getting lost, searching for parking, etc. If you're not yet interested in fares, you can get schedule info from the user-friendly Deutsche Bahn website. To see fares you can go to Renfe.com, but note that the express-train fares will vary, depending on how early you buy your tickets.

The only part of your itinerary with super-fast train service is the Barcelona-Madrid link. For that one, the AVE train (as fast as 2 hr. 45 min.) will be much, much faster than a car, and it will also avoid parking issues (and costs). But you'll pay through the nose if you wait until the last minute to buy those tickets.

Between San Sebastian and Bilbao you have two public-transportation options. There's frequent bus service taking, I think, 1-1/2 to 1-3/4 hours. I'm having computer difficulties at the moment, and the ALSA website is non-responsive. There may be other companies doing that run, but ALSA is a large company that does have service on that route. The buses are very comfortable.

There is train service run by Euskotren, but--though quite scenic (at least in the summer)--it is much slower, taking about 2-1/2 hours. I've linked to the winter schedule. It looks as if the train basically runs hourly. "Donostia" is the Basque name for San Sebastian. If you're struggling to figure out the text, half of it is Basque.

Because of the excellent bus service, there's no need to rent a car just to move between Bilbao and San Sebastian. If you want to travel around the countryside, it might be advantageous.

There is no express-train service between the Basque Country and either Barcelona or Madrid, nor are the trains frequent. Traveling from Madrid by train, it doesn't make much difference, time-wise, whether you head to Bilbao or San Sebastian, so see whether there's a departure time you like that also isn't unduly slow. From Barcelona, San Sebastian is a quicker trip.

A car may save you a bit of time between Madrid and the Basque Country--or not, depending on your luck with traffic, finding parking, etc. I'm a train fan and would stick with that if I didn't need a car because of plans to visit smaller towns.

The Basque countryside was lovely during the summer (from buses and trains), but much of what you'll see closer to Madrid is, frankly, dull. I'm sure that applies equally, whether you're on road or rails.

Check historical weather stats for your destinations. Madrid can be rather cold in December, and the Basque Country tends to be overcast and damp, though not as cold as Madrid in the winter.

Wow! Carlos, Acraven, Nick, thanks for this! I'm going to dig into your recommendations today and will hop back on with my results, but just a big thank you for all of that info (and your time)!
Bruce

Carlos, thanks a million! We've been digging up the info on your suggestions. We'll be driving from Barcelona to S.Seb, and taking advantage of the places you pointed out. We're definitely doing most of your suggestions. You saved us a lot in research. Many thanks!

Acraven, ditto, thanks for all the recommendations! We'll be utilizing that for our train portions.

You guys are awesome!

Bruce, glad I could help - have a great trip! :)