The fastest drive between Barcelona and San Sebastián is all highway and not scenic, at least not before Pamplona.

Much more scenic if you go a little north, winding through the Pyrenees and allow for some sidetrips along the Lleida, Huesca, Jaca, Pamplona route. But it will take you several more hours (and you would probably want to stay over in perhaps Biescas or Torla).
Torla: https://www.google.no/search?q=Torla...w=1600&bih=754
Hotels in Torla: http://www.booking.com/city/es/torla.en.html

Along the fastes way, I would have stopped for lunch in either big Zaragoza or small Tudela. Both have a rich history (both for instance 400 years under muslim rule), interesting old towns and sights and of course plenty of genuine tapas bars and restaurants.
http://wikitravel.org/en/Zaragoza
http://www.spain.info/en/ven/otros-destinos/tudela.html