Hi! My wife and I went on Captain Marv's two-hour Stingray City tour off of the Triumph on Apr. 9th. I had booked this over the internet for $34.00 pp.
It was a great tour, approx. 20 people on a large cabin-cruiser. Informative guide, clean and modern snorkelling equipment, bottled water or punch on board, etc.
The boat stopped at a reef for 20 minutes of snorkelling for those who wanted to, and then moved on to Stingray City, which is as spectacular as everyone says. My wife who is extremely wary of water enjoyed it immensely, as did all others on the boat.
Each adult on the tour got a free small rum-cake, and 10% off in the gift shop, which was not over-priced.
Bear in mind that the Cayman's are one hour behind ship time--so an 11am departure is 12 noon ship time. You will not come back from this tour until about 2:30 ship time, which only gives you 1 hr. to catch the tender back to the ship (if the last one departs @ 3:30 p ship time. So do your other sight-seeing in the early morning.
PS: Don't save your shopping for GC--it is very expensive, and their dollar is higher than the US. Buy a couple rum cakes, they are great.
Have a great time, Tim