Do one of those tours - only, and only if, you have done the Sting Ray city before - this is a "must not miss" tour. Believe me, you will never see anything like this ever! I was a little nervous about taking this tour, would it be scary, would I get stung, etc. but had so many people tell us before going to Grand Cayman to make sure we did this so I thought I'd give it a try. We've been on 8 cruises all to different ports - I don't think there's beena port I haven't seen and this by far exceeds anything I've seen in the other ports.
I hope this is not inappropriate but years ago on the Holiday in the Caymans I was on crutches with a knee brace so the only excursion I could take to see the ocean in all it's glory was the glass bottom boat tour. The waters were so choppy that people were having to jump to the tenders. I couldn't jump so I couldn't get on to the tender. I couldn't take my glass bottom boat tour. Guess what! The glass bottom boat hit a reef or rock (can't remember which) and broke the glass through. All passengers had to be rescued from the water. No one was hurt.
They are like puppies in the water - believe me, not a lover of anything with Stings but this is something you will not believe. At first I thought I'd be scared too and almost didn't do this excursion but take my word and the word of many, many posters on these boards - don't miss it!
I've done the glass bottomed boat tour and thoroughly enjoyed it. The coral around GC is beautiful and they take you over an old lumber freighter which sank in a hurricane. Trip only lasted 1-1 1/2 but very interesting and inexpensive. But, as the other posters mentioned, I've also heard Stingray City is THE place to go.