Search and compare
The two services are essentially the same thing in terms of the way they work. Valet parking tends to be the airport's own doorstep service which will normally involve leaving your car at a kiosk outside the terminal entrance. Meet and Greet (although also offered by the airport) is more likely to be an Airport Approved operator working from the meet and greet zone. The meet and greet zone is also just a short walk from the terminal entrance / exit.