Stayed at Sheraton Riverwalk. Very friendly staff. Nice room. Great river view from room balcony. Free shuttle bus to the port made it really convenient for us. We visited Busch Garden before the cruise and totally enjoyed the theme park.
We signed up for the Hell, Turtle Farm, and Sting Ray City Tour by Carnival. We love all 3 places, especially the Turtle Farm. However the pre-tour wait (under the hot sun) was pretty long, and too many people on the same boat to Sting Ray City. We wished we had arranged this tour with other independent vendors.
We've been to Cancun before, and have already done activities like dolphin swim, ruins, etc. So we hired a taxi to Paradise Beach (also a great tip learned from this board. Thank you, CruiseCritic!). We all agreed this was be best excursion during our cruise, and it cost the least.
We went cave tubing with cave-tubing.com. We paid half the price than the ship-organized tour and a much pleasant experience. Smaller group, no waiting, better guides! Highly recommend cave-tubing.com.