I got married in Fiji and loved it. We took some of our family over with us and had a blast, so much so that they now head over by themselves for their own holidays. Fiji is a beautiful destination and there are so many gorgeous islands to choose from. We chose Sonaisali Island and as perfect as it was, I think it was a little bit out of the way of Nadi. Perhaps Denarau Island, there are many resorts there and its close to Nadi and the port where you can take trips from.
Good luck with your decision and congrats on the wedding.
PM if you would like any Fiji tips...