I have used the valet service companies a few times.
WINNER and PACIFICO are next to each other on Essington Ave
You drive to their site then they drive you in your car to the airport.
When you return they pick you up in your car.
Usual practice is then to go back to their office to settle up $
For an additional fee can leave from the airport without returning to their office
Advantage: no shuttle bus and moving luggage extra times
With taxes and fees ends up about $10/day
I just checked all the recommended places from this thread...Wallypark, The Parking Spot,
PreFlight, were all more than Pacifico valet for my six day trip next week. Winner and Pacifico were equal or better than the services with the shuttle bus. I give a bigger tip to the valet then I would give a shuttle bus driver (depending on quality of service, baggage help, ...etc...) but even with that the valet services have the bus services beat on $