I cant comment on Fiji, that's on my travel and dive list for sure. I have been to Tahiti in late 2013 and we stayed on the island of Moorea for two weeks. We landed at PPT on the main island of Tahiti, took a cab to the catamaran terminal (10 min, if that) and walked on that for a quick boat ride to Moorea. Not sure what the other islands are like, but Moorea was super laid back, I really enjoyed it. I would compare it to Kauai.
I did my pool dives and classes in Canada but did my OW dives there to get certified. We dove with Moorea Fun Dive which is on the west coast of the island and the owners are Christian and Marie, at the time they had just taken over the operation and they are fantastic! We did 8 dives with Christian, the first OW dive we saw a couple Lemon Sharks, tons of black tip reef sharks, a Great Barracuda (still the largest I've ever seen) many other little critters which at the time I couldnt identify let alone spot without the help of Christian pointing them out. Did a drift dive to see the Spotted Eagle Rays, another dive called the Canyons and one other to check out the lava flow from the extinct volcano. The visibility was fantastic and when we were getting certified Christian had joked that we're having dessert first by kicking off our scuba diving in Moorea.
We rented a few VRBO's for most of the time there (
tbd-rentals was one of them Moorea07) and the other was called Fare Hamara, but I dont think they're renting it anymore

we also stayed at the Sofitel Moorea Ia Ora, which is very nice. You can snorkelling right from your room (or the beach) and the water is super calm at Temae beach.
There is lots to do on Moorea other than scuba diving, you can rent jetski's and go feed sting rays, go quadding through the island, tour some of the plantations, snorkel, just soak up the sun on the beach and lots more. The food is fantastic there, quite a variety of restaurants (even a burger joint owned by fellow Canadians with a burger that is not to be taken lightly). I dont think we had a bad meal the entire time.
As you can see, I cant reccommend it enough, cant wait to go back, but next time I will be spending time on some of the other islands like Tahaa, Raiatea or Bora Bora