Meet & greet. Your driver parks, walks into the terminal, and waits in the arrivals hall holding a board with your name on it. You meet them there and they walk you to the car. This is the simplest option after a long flight, with luggage, with children, or if you do not know the airport. It usually carries a supplement because the driver pays to park and spends longer at the airport.
Car park meet. Your driver waits in the designated pickup area — typically the short-stay car park attached to your terminal — and calls or messages you once you are through. You walk to the car park, find the level and bay number they give you, and meet them at the vehicle. It costs less and works perfectly well if you are travelling light and are comfortable navigating the airport.
Neither is better in the abstract. What matters is knowing which one you booked, because arriving expecting a driver in arrivals when they are actually waiting in a car park is where the stress starts.