Bugsy, my wife and I spent 17 days at Blue Lagoon Beach Resort on Nacula at the upper end of the Yasawas. I did three dives a day nearly every day there and realllly enjoyed it. This stay was on the tail end of 9 weeks in Fiji. I dove Naigani, Matava on Kadavu, and with Bega divers while staying in Pacific Harbour. Of those four places I would say that the diving was best on Naigani with Matava, next and then Blue Lagoon Beach Resort and last was Pacific Harbour.
That being said, during the rainy season I would definitely return to Blue Lagoon and not take the chance on the weather on the rainier side of Fiji. The weather was GREAT at Blue Lagoon in late Nov and early Dec. The staff was fantastic, the food was extremely good and the atmosphere was the most fun of any of the places we stayed. Meals everyone eats dinner at the same time at large tables and it is easy to get to know the other people there. There is something going on nearly every night. From crab races, to "Survivor Fiji" competition (the table that wins this is treated to a champagne breakfast on the beach the next morning) a bonfire one night.....just always something fun going on. My wife doesnt dive and she LOVED our time at Blue Lagoon.
The diving at Blue Lagoon is really very good when compared with the non-Fiji places I have dove. It beats Kauai and St. Thomas hands down. The reefs were in very good shape. During the regular dives I saw Christmas tree worms, sharks, barracuda, lobster, sea snakes, turtles, lion fish, a couple of different kinds of large crab, cabbage coral, and the list goes on and on and on. There are a couple of dives sites with excellent canyons and long swim throughs. Twice a week they do shark dives in conjunction with two other resorts and it is a fantastic experience.
Now Blue Lagoon is not first and foremost a dive resort, but they do three dives a day and night diving is also available. Their dive packages are a very good value and they never hesitate to send the boat out, even if there is only one diver that wants to go.
Now if you are going to strictly dive dive dive dive dive and nothing else matters........AND you are not going in the rainy season, I am sure you would be happier with Naigani or Taveuni or Kadavu or some place that dives the Bligh waters. But from what you have said in your posts I think Blue Lagoon would be just the ticket for you. The Yasawas are great for backpackers and island hopping and our experience at Blue Lagoon was top notch. Many of the people we got to know and socialized with in the evenings were singles and many were backpackers.