Great location and easy access from terminals. Good selection of cars in the Emerald Aisle, and reasonable rates. Great customer service and quick return. The car I rented was a little bit older and was showing some wear and tear but a great drive regardless.
National, in general, is my absolute favorite car rental agency. Being able to go directly to the cars, pick out what you want, and go is awesome. Similarly, returning the vehicle is even more painless and about as fast as humanly possible. By the time you can get your luggage out of the car, you are checked out and have a receipt in-hand. On my latest trip to SFO, the car selection was a little limited, but that is more a function of timing than anything. Fresh cars were constantly returning to the lineup, so within a few minutes, you can find something you like. In my opinion, the best customer experience in this business.