We spent three nights at Momi Bay Marriott, two nights at Likuliku in an over the water bungalow, and then three nights at VoliVoli, which is a dive-focused resort. If you aren't going to dive, then skip Volivoli - it's too far out of the way and on the dry side of the island. The diving there is world class though. Most divers on our dives were very experienced divers who had been wanting to dive there for years.
Likuliku Lagoon Resort is an idyllic Fijian destination for a romantic vacation for couples only, island trips and scuba diving in Mamanucas.
https://likulikulagoon.com/
Momi bay Marriott is a very nice resort, but it just felt like a normal US resort. Very similar to going to Hawaii in my opinion.
Likuliku was AMAZING. When we took the boat ferry to Likuliku, it made stops at many little island resorts along the way.
If I were to go back (and I want to very badly), I would stay the whole week at one or two results on the little islands off the coast of Nadi (similar to Likuliku but more afordable than Likuliku) like any one of these:
There are so many little islands and most of them have a resort on them. Fiji is amazing.