Returned last month from 4-night stay at the Riviera Marriott. I believe that if you're intersted only in what is happening in Monte Carlo, you can definitely get away with just relying on the hotel's free shuttle service. However, if you're going to make day trips to Nice, Eze, et al, you would do well to rent a car; this you can do through the concierge in the lobby (EuropeCar). I wanted an automatic that I had to get from Avis in Monte Carlo. Shuttle staff is quite accomodating when it comes to picking/dropping off guests near normal routes.