The airport at Cancun has several car rentals at $40 a day - includes MX insurance. Best to use this service so that you can go around Cancun. The hotel zone is 1 strip of hotels and the I think this is the cheapest mode - at least, you have a car at your service once you get there.
Get a car from the airport - drive to your hotel and have the car to your disposal at all times and then return the car to the airport when you are ready to fly out of Cancun.
PRO: no need to wait for the local bus, no need to hire a taxi cab, no waiting for your shuttle pick up... you can go to the 7-11 24hrs stores anytime of the nite..
CON: not much except to learn how to drive the local way.... buy gas....
Cancun Shuttle offers private rides to and from the airport to your destination. The driver nor the greeter do not make sales talk about properties (time shares) and tours in the area - which is very nice instead of constantly saying "no" to their efforts.... We used their service on our 2nd trip (jul 2006).
I've arranged for Best Day Travel to pick us up to and from the airport of Cancun and take us to the hotel. It is a shuttle company.
The fare was $20 each person for the 2 trips -plus recommended tip to the driver.
Very good experience since it is our first time. Taxis were not recommended by other VT's but I guess we can do the taxi next time since we now know the way to the Hotel Zone. Taxis were $15 to the hotel area from the airport.
The only catch is that at around 2 hrs after dropping you off, a rep will have to meet you to get your return itenerary - verify your tickets and advice you the time of your pick up - and of course, sell you a tour....
But not a too pushy rep came to us though....They also offere other tours in Cancun.