Best diving on Nananu-ira or Ovalau?

Just over a week before we are off. We will mainly be snorkelling but may splash out and do a scuba dive. Would it be better diving (looking for big fish, rays, spectacular coral and good visibility) from Nananu-ira or Ovalau?

two areas that are quite different but both are very nice
reefs around nana nu ira are very colorfull with plenty of softcoral, seafans nice canyons, not so much big fish you may see a whitetip ever other dive...
reefs around ovalau are more hardcoral, there several narow passages that have lots of big stuff, rays and sharks are common.