On
Grand Cayman's Sunset House, you will find an ideal place for a vacation with some diving. Lots to see and do, many restaurants, acceptably scooter safe (right hand drive/wrong way) roads, available medical facilities, superb beaches, it is truly a theme park for divers. You can walk into town, but 7 Mile Beach is a bit further and still walkable. It is one of the few original (70's) resorts that remain on Cayman that are biased heavily towards diving.
Sunset &
Cayman Island, generally,
On a Caribbean scale: Beaches (a long walk) 9; Cost 7; Island Prices 10; Topside Diversions 8.5; Dive Services 10; Reef Health 3.5; Critters 3; Lodging 8.5 (motel-ish); The House Reef 1
Roatan's AKR is an established
AI Resort with a well run dive operation, not much to do within walking distance other than dive. (This applies to almost any other resort option on the island, you're cabbing it to night life). It's a good place for a Dive Vacation, unfortunately the sand flies are rife on the Bay Islands and the roads really suck. Driving is ill advised.
This (Northside) Resort and nearby Roatan,
On a Caribbean scale: Beaches (cab ride) 1.5; Island Prices 1; Resort Cost 3; Topside Diversions 1.5; Dive Services 10; Reef Health 7; Critters 7; Lodging 6>7 (modern jungle cabanas); Shore dive (house reef) is really a non-starter 0
You can learn a lot more about AKR/Roatan or Sunset House with a simple

and a bit of reading in the specific forum.