Sugestion 1) Move from the Hilton... OK, it a very nice hotel, but the diving on that side of Fiji is not our best. Fun for something to do in the morning, but not worth coming to Fiji for..... That is if you are really into great dives.
Now there are some nice dives around there, but if I had the choice, I would move around a bit. So....
Options.
If you are prepaid at the Hilton, don't worry. You can do day trips down the coast to do the Shark Dive with Aquatrek - very cool - and maybe a days soft coral diving with them too. It takes about 2 1/4 hours to get there by taxi (cost about FJ$200 return - haggle with a local taxi rather than book with the resort if you want to save a fair bit on the fare.
Do you surf? If so, 2 world class options of Frigates passage and Cloud Break both day trips. Frigates is also a cool dive. (book through Waidroka resort)
Head the other way around Viti Levu and you can go out with Wananavu or Ra Divers for a day in the Vatu i-Ra passage - seriously cool walls and big pelagics, often drift dives. About 2 1/2 hours to get there. Make sure they are planning to go to the Vatu-i-Ra that day before you go as they don't do it every day.
A little bit closer to Nadi is Scuba Bula - now I have never dived with these chaps, but they offer some interesting sites.
There is a dolphin snorkeling day out based at Takalana. A bit harder to get to but very cool to swim with these Spinners.
If you did decide to move from the Hilton, then there are loads of options depending on your preference for accommodation, price, diving and activities.
I hope that gives you some food for thought. Let me know if you want any more ideas or info.
Let me know if you want any more suggestions.
Cheers
Greg