On the 7-day itinerary, we did Pacific Grill on Tuesday while at anchor at Bora Bora, and La Verandah on Wednesday. This worked fine for us. I enjoyed the food and ambiance of both. Some people like to eat dinner off the ship at Bloody Mary's in BB - if that possibly interests you, you would not want to reserve a specialty restaurant for that night.
I enjoyed eating outside at Le Grill for the tropical open air feel and breezes. Chances are it will be dark by the time you eat, so there's not really a benefit in terms of scenery or sunset viewing, unfortunately.
The really cool thing is that if you miss something you really like in the main dining room, just make a special request with the maitre d' and you can have it another night. Also, on the night they have lobster in the main dining room, they will also have lobster as a special in the other restaurants. Seems nobody wants to miss out on the lobster (well, except me :) )
Dena