I've rented a car at the airport for both stays, and found it to be a much less expensive way to get out for sightseeing (a very easy, straight drive on the highway to Chichen Itza, a local zipline/cenote tour, Tulum, etc.). And in terms of cost, it was cheaper to rent a car for the entire stay than to pay just for the car service to/from the resort, let alone excursions. But of course, if cost isn't an issue, it's always nice not to have to worry about picking up and returning a car. I'd just always prefer to use my money for the resort, food, etc., and not for transportation. No idea about sat nav.