Looking at some other threads, I have a choice of either

The Westin Denarau Island Resort & Spa, Fiji
or
Sheraton Denarau Villas

I want to go diving, and from what I read the Westin is pricey. Has anyone else went diving? Should I stay in the Westin or Sheraton or go to another non-SPG hotel resort for diving?
Also, upgrades for gold in Westin or Sheraton?