Dominica. One of the world's most beautiful islands topside, very few people, very few tourists, spectacular diving in the south, excellent diving mid island on the Caribbean side, some good diving in places in the north, including at least two excellent sites, and so much fish life it can seem unreal. Not just the usual stuff: things you never or seldom see in more frequently dived places. It's like St. Vincent in that respect, but easier to get to. There are now two carriers to Dominica. One, LIAT (luggage in another terminal), I'd stay away from. The other, Seaborne, recently took over the San Juan hub from American Eagle. It's based in the US Virgins, and I'll be flying them for the first time in April, when I'll be staying in Dominica for most of the month. Both carriers are expensive.
Dominica is not for everyone. It rains frequently, and it's a volcanic island, so boulders outnumber coral heads. The roads are horrible, but I've always driven a rental jeep there, though most Americans are too fearful, wetting themselves when they look down 600 feet through sheer air from a road that corkscrews on the side of a mountain with just enough space for the tires. I also rent my own little villa (very cheap) and spend a lot of time topside in a mountainous rainforest like no other in the Caribbean.
The diving is nearly pristine, and I've seen everything from unnamed tiny gobies up to and including whales while snorkeling. When scuba diving the array of wonders can be even more
impressive.
Dominica is different. Feels different, looks different, smells different, especially if you get away on your own from the two or three dive dedicated operations in Roseau for more than just the one or two afternoon expeditions they sponsor for their captive divers.
I agree that St Croix has some very nice sites. Saba is amazing but deep. Very deep, every site. It's something like North Carolina in that respect. St Thomas and St Kitts are, for lack of a better word, meh. Expensive meh. Dominica is hellishly expensive to get to, but pretty reasonable to downright cheap when you get there. I usually go once a year, for about 3 to 4 weeks.