I just rented a car from Alamo at SNA this past weekend. This airport rental car situation is the best thing since sliced bread. Everything is right there on property, in a parking garage set up especially for rental cars. All the majors are there. Alamo and National are together, there's Budget, Hertz,etc. They are so easy to get to. You go out of baggage claim follow the signs to Ground Transportation and walk down the sidewalk, follow the signs to your rental car company (half are on one side of the garage the other half are a little farther down), cross the walkway, take the elevator down to the rental car companies offices and the cars are right there waiting for you. It took me all of 15 minutes to go from baggage claim to driving off the airport property. What a dream! Especially since I had got an Alamo compact for $12 a day (Chevy Cavalier) which was perfect for hubby and me. Gas was $2.25 a gallon but we only drove from the hotel and back. (At $12 a day for 2 days it was cheaper and more convenient than taking the Airportbus or a shuttle).
John Wayne Airport is wonderful. One of the easiest to get in and out of. Just remember that they have 2 security areas set up. On Sunday afternoon the line by the Southwest counter had about 75 people in it while the one by Continental/AA, etc. only had about 15 people. Don't forget when you are leaving.
Hope this helps. JWA was great and when we flew out we went right out over the shoreline, it was beautiful!
PS Because of noise abatement issues, the planes pull up rather quickly out of JWA after takeoff.