I thought about suggesting Grand Cayman also but first dives there are often deep down the wall. However you can tailor some of it to a newer diver by finding the right trip/operator. 2nd dives on a two-tank morning trip will be done shallower. Many run afternoon trips to shallower sites - often they do their cert. dives then also. Still good dive sites, Aquarium was one of the better dives we did - it was 45' to the bottom.
Also Turtle Reef is another must do shore dive - if you want to do it guided, there's a
dive operator there you can arrange that thru. It's a great dive, shallow vertical wall that bottoms out in the sand at 45-50'. To the south there will be a school of tarpon hovering in a recess in the shade - they've been there for years.
Same with Sunset House and Divetech/Cobalt Coast - the other two dive resorts on the west side. Both have easy, shallow dives off their property - and offer boat diving as well. Cobalt Coast is in a quieter residential area on the north side of the island, Sunset House is in south Georgetown. There's also likely to be 2-3 cruise ships in port there daily so staying on Seven Mile Beach might be a better option. All of the dive operators have a free shuttle in that area.
Most dive operators on Cayman (except the cruise operator) will do 6-8 divers max
per boat, some like Ambassador Divers will often go with 2. All are required to put a DM in the water for every 8 divers also. Personally I enjoyed Cayman more than either Bonaire or Curacao - it's much more dramatic wall diving. And you're likely to see bigger things there. And there's Stingray City - the best dive you can do in 15'...
Dive operators that are often recommended in the
Cayman Islands forum here on SB:
Ambassador
Wall to Wall
Neptunes
Living the Dream
Divetech
But really they're all good. Cayman is such a competitive market that bad ones don't last. Also since so many divers want to work there, chances are good your DM will actually be an Instructor.