Narrowing your choice down to SPG or Hilton within the pacific, will limit you choice. Often some of these larger chain hotels are in the less desirable locations..

The Cook Islands (Rarotonga) only have an once weekly flight from Sydney on NZ, but atleast 2-3daily from Auckland on NZ,VA,JQ.

The main Pacific Islands are:

Tonga
Samoa
Fiji
Cook Islands
Tahti (ex AKL Only)
New Caledonia

Outside of Fiji, Sydney has limited flights to the Pacific Islands. We're you might find for some days of the week you'll need to route via Auckland.