Another vote for this. I have just them for about three years now.
You can see the drivers with their orange signs standing together near the exit door the moment you come out of the door after you walk past the customs area.

The prices for a Mercedes S or Mercedes E class car is rather good compared with elsewhere in the world; particular when you book their "sale price" on-line

You get a little Prague guide book as you arrive at your hotel. The drivers speak reasonable English, are polite and well-dressed.