I always use Skypark valet on Fasken Drive.
Its $10 a day, or $50 for 7 days.
Drop your car off and pay, they drive you to the airport. Then when you get back you call the number and they pick you up and bring you back to your car.
Been using them for years and always happy with the service. Skypark Airport Parking, Toronto Pearson Airport's Best Kept Secret