We used cave-tubing.com in December and I can't say a bad thing about our tour. They picked us up inside the port, the guides were very entertaining and personable, and the excursion overall was a lot of fun. Was a relaxing stroll down the river, so, not going to be as exhilarating as zip line for sure. My opinion is: Do the zip line in Cozumel and cave tubing in Belize. And unlike what denjoker suggested, cave-tubing.com is an off ship tour company. We paid half the price of what we would've on the ship. Didn't have the "insurance" of booking thru the ship if something got delayed, but it doesn't seem like that is an issue at all. We were under no duress at any time to make it back to the ship. You'll have a great time no matter what you decide!!