I used the shuttle to and from the Puerta Juarez ferry because we were staying on Isla Mujeres. If you go to the islamujeresnet site you get a discount code for Discovery Mundo. They were waiting when I came out of the arrivals section at Cancun. We had to wait about 10 minutes for the driver because the private shuttles are not allowed to wait in the arrivals parking. When we were coming back from the island the driver was there waiting for us. Easy. Much better than haggling with a taxi driver or another shuttle service or waiting for a bus.