Folks,
Just wanted to report in on our experience renting in Spain.
We used National/Alamo/Atessa. Good rates and good service. ( Service at Saints train station in Barcelona was a bit discombobulated, but 1 marginal experince out of 4 is pretty OK for Car rentals..from my experience.) Their Website is fairly easy to use, and the phone support is good.
We rented twice, one ways from BC to San Sebastien and back.
Spainish highways are well engineered with minimal traffic. Tolls are HIGH. We spent 45 Euros each way. Fuel was only slightly more. Distance was about 300 miles each way.
In short; If you like to drive on vacation, Spain is fun and easy to do.
Good luck!
Rog Smith