Hilton Moorea or L'Tahaa for activities, snorkeling, alone time, and sheer beauty
For sheer beauty, it really depends on what you're looking for. They are both beautiful.
BUT for snorkeling and alone time, you can't beat Le Taha'a. The drift snorkel right off their motu is unique and amazing and Le Taha'a is very private since it's on a motu. In fact, the entire island of Taha'a is much more quiet and secluded than Moorea.