Anse Chastenet on St. Lucia seems to fit your requirements. The break the budget resort is
Jade Mountain - above it on the hill. There's other resorts on St. Lucia that will also work - these are just two I looked into once. Good diving also - I personally haven't heard that about Antigua - IIRC the resorts are located on the other side of the island from the best of it.
The Westin or the Marriott Grand on Grand Cayman also maybe. One advantage there is Red Sail Sports is onsite for diving and other water experiences - plus if you don't like them - there's about 2 dozen other dive operations that will pick you up there. In the heart of Seven Mile Beach which is georgeous. Maybe busier than you sound like you want.Also Cayman is very pricey - boat dives are over 2/$100 - offset by some really good shore dives and food is outrageous at any of the restaurants near the water - it's all imported and the CI$ is fixed at .80US$
Cayman diving is among the best I've done and that list includes many of the Caribbean dive destinations. Deep walls surround the island - in 2 places you can surface swim out to them and tehy've really embraced diving - Dive365Cayman.com lists 365 moored dive site options. IMO the best is the sites on the north wall/west bay area but I haven't dove the east end. Videos also of most of the sites to see what they're like.
There's also a lot of fun dives, the Kittiwake is a dive cleaned wreck in shallow water - it's a big boat but dropped deliberately so the top can be snorkeled. So shallow that recent rough weather moved it from vertical. Stingray City is the best 15' dive you'll ever do - get mobbed by rays for 45mins. And Turtle Reef on the north side may be the best shore dive - it's near the turtle farm so they occasionally get out and live there on the reef. There's a 60' deep mini-wall that's loaded with stuff and a tarpon cave to the south - move slowly and you can swim among them. We were there in late March/April and the weather was nice - sometimes in the winter the north is undivable.
My short list of goto dive operations is Neptune's Divers, Ambassador Divers or Wall to Wall. But there isn't a bad operation there - competition is too great. One thing to look for is the 6-8 divers max. operators - many have boats for twice that many. Makes for very comfortable rides. Many of the better sites are 10-15 minutes from the marinas and they all include van shuttle service from any resort/condo complex on Seven Mile Beach.
It or Provo in the Turks/Caicos are the most expensive places we've dove. In our case a LOB trip minimize the T/C expenses. Grace Bay Beach is one of the nicest I've ever seen but resorts on it know it. Also the best diving is about an hour by boat away so that often limits dives to 3/day - there's no shore diving there. It really is a stunning island though in most areas.
If it's re-opened before your wedding
Little Dix Bay resort on Virgin Gorda is as nice as it sounds. I've not stayed there but had drinks at their bar. Also we dove with DiveBVI all week and several times went in there to pickup guests - turtles dove for the bottom when we did. Hotel guests can snorkel safely as there's only one boat channel in/out - the rest is shallow coral reefts. It's pricey though.
Nice diving there, snorkeling at the Baths etc. Better restaurants than you'd expect for a small island population - it's because there's a lot of large villas so that attracts money. It's a pretty unpopulated place - LDB has a catamaran (they'll pick you up at the Tortola airport with it) and will drop guests at private beaches only accesible by boat - no road - with a picnic lunch.
The island took a big hit during Irma also so IDK how the recovery is going. LDB was scheduled to re-open after renovations next week but they've had to delay that due to new damage. It's a Rosewood property so hopetully they have the resources to rebuild.
