If you are flying to Andorra, you surely arrive to one of the major airports that serve it - Barcelona Airport and Toulouse Airport (other close airports are Perpignan and Girona Airports). You can rent a Mercedes at Toulouse Airport or any other mentioned above airports and drive to the Pyrenees ski resorts in Andorra in style.
Pas de la Casa (& Grau Roig) - one of the known resorts - accessible from the capital, Andorra la Vella.
Vallnord is closer to Spain's border and linked to Pal and Arinsal sectors.
Soldeu is a skiing town - near to the Grand Valira ski resort, the largest ski resort in the Pyrenees.
Other ski resorts in Andorra, available for Mercedes rental are Grandvalira, canillo, La Massana and Encamp.