Fiji - in 5 days!

Hi folks,
I have 5 days in Fiji at the start of June, would love to stay longer but am constrained by time.
Were would the best place to base yourself be....am flying into Nadi. Would like to experience fiji culture, quiet beeches and maybe a tour around some of the islands. Am a backpacker..but would mind paying a bit for accom.

Thanks very mucj for any help!