I agree with Tim that I've consistly seen more barracuda, rays and sharks in the Caymans. But in Roatan, grouper and many kinds of angels were bigger and more numerous than I've seen in the Caymans, including some astoundingly populous schools of sargent majors. Also, I've never seen seahorses or wild dolphins under water in the Caymans but did last week in Roatan (the latter is just luck in either place).
I'll still dive the Caymans (maybe as soon as as mid-January if some friends have their way) but I'd say Anthony Key's Resort is the best run dive resort I've seen. It's very user-friendly and nothing goes wanting. They don't overplay ridiculously load music to 11, as Little Cayman Beach Resort does. And instead of bulldozing the forest for a hotel, they have little bungalos spread around, with or without a/c. Easy on the land and cheap to build after hurricanes.
I usually pay around $2K for a 7 night stay in the Caymans. I got a week of 3 boat dives, 7 night stay and unlimited shore dives with room, board and airfare to Anthony Key's from DC for $1100, although it was in a low demand period. Of course, with a rare Washington DC snow storm it took a day and half to get there (and a tour through El Salvador and Honduras), but that's another story.
Also, the food's better at AKC than at Little Cayman Beach Resort of Divi Tiara. My buddy had to cancel, and they didn't raise the rate for my single occupancy tree house in the rain forest overlooking the sea.
I'll be doing nearby Utila in Feb. for whale shark season and will post how that rates.