You probably already have your car secured, but just wanted to let you know that we used AutoEurope while we were in Spain last fall. They are a rental car consolidator operating in the US, and what I really appreciated about them was they are willing to meet competitor's prices. Their prices were also fairly low, although I'm not sure what they charge for a different drop off site. Through AutoEurope, we rented using Avis. (Had we rented directly through Avis, it would have been more expensive.)
When renting a car, I was concerned about comfort and luggage space. We were doing a 2 week road trip and my S/O is 6 feet, so room and comfort was a biggie for us. We ended up with an Opal Zafira - something a lot of people told me would be far too big. In reality? It was just perfect! Roomy on the inside, comfortable, terrific handling, and wonderful on gas, yet seemed like a small car. Our only difficulty driving was in Madrid and Seville. Other than that, everything was fine. Would a smaller car have meant easier parking? Doubtful, really. We would have had to sacrifice comfort and been irritable with each other. Glad we had what we did.
We could have fit two more people in the car, easily, though luggage would have been a bit more difficult and we probably would not have been able to cover it.