By far my favorite tour was the lagoon tour and motu picnic. I used Hiro tours and they will pick you up. The Lagoon is incredible and must be seen by boat. First stop is a stingray feeding in waist deep water. The guide will give you some fish bits to feed the stingrays with. They are the puppy dogs of the sea. Next stop is a different area where the guide will feed the reef sharks. Guests hang onto a rope to watch from a little further away. This is not for people afraid of fish because the sharks will swim right in front of you. The motu picnic includes some lunch and rum punch. Or you can spend your time swimming & snorkeling.
My other recommendation is a circle island tour.
Sofitel- view of the bungalows in turquoise water
Belvedere Lookout- Cook's & Opanuhu bays from inland
Fruit Juice factory & free liquor samples
Another good option is an off-road tour. You would see Belvedere Lookout, the juice factory and more of the island interior. Last stop is Magic Mountain where you can view Cook's Bay from high up.