I think a ship is a great way to see the Society Islands. You want to see Tahiti just because it is Tahiti, and the same with Bora Bora. Moorea is a truly beautiful island, and so it is worth taking a cruise just to see those three.
To me the beauty of the islands is in seeing them which doesn't require a week. I feel the same way about Hawaii - I wouldn't personally want to stay a whole week in one place.
It depends on your temperament, however.
It is a long way to travel, so it makes sense to spend extra time, and there is nothing wrong with seeing Hawaii on the same trip since it is "on the way."
We spent a week on the Paul Gauguin and absolutely loved it. Awesome way to see the various islands and of our 43 cruises is our all-time favorite - hands down the best ever!
Afterwards, we spent a week on a private island that was wonderful.
Both were extremely enjoyable for different reasons and I'm not sure I could decide between the two as to which one I liked the most, but if nailed to the wall, I'd have to lean more towards the cruise - just more to see and more to do.
As for which way to go, it's like Paul said, it really depends on your temperament and what you're more leaning towards.
Personally, while I really enjoyed the laid back relaxation of staying in the same place, I also really enjoyed visiting the various islands, trying different foods, seeing the various cultures, and hearing about all the history.
If you do decide to stay in one place, I would not recommend Tahiti. Instead, I would suggest looking at Bora Bora or Moorea. Keep in mind that getting to Moorea is cheaper (about $15 each way) and easier as there are ferries that make the short trip regularly during the day. Plus, the resorts are on the main island. There's also several places on the island to eat and/or shop. Whereas if you go to Bora Bora, you have to fly and the 45 minute flight will run about $450 per person roundtrip. There are very few places to eat and/or shop, but all the resorts are located on the motus surrounding the main island, so you have to take boats to and from the resorts.
But no matter what you decide to do, I know you will thoroughly love every minute of it - it's truly a magical place and it's as beautiful as any of the pictures you've ever seen.
__________________ Travel Agent/Cruise Specialist w/13 yrs exp and 48 Cruises on 11 cruise lines! Favorites: Paul Gauguin - Tahiti: Uniworld River Cruises - Europe; Celebrity Solstice-class ships; Holland America - 12-nights Baltics & Russia; RCCL - 14-nights Greek Isles, Turkey, & Croatia; Holland America - 14-day Alaskan cruisetour; 10-night Canada/New England cruise; 21 days Hawaii w/7-night NCL cruise; Oceania - 25 days in Asia; more than 3 months touring Europe by train. And many all-inclusive resorts!
You will have a wonderful time and Oceania is a good choice.
The island of Tahiti is ok but the outer Society Islands are what will give you that true tropical paradise. I hope you have some overnights in the itinerary. A great way to see Bora Bora is to rent one of the small cars (basically a golf cart) and explore the island. Stop by the roadside stands and small markets and restaurants. You'll have a ball. I agree with Jean that it can be a bit expensive so plan on eating your breakfasts and dinners on the ship but do try some of the local food for lunch. Or just grab an assortment of tropical fruit from a roadside stand and have a wonderful lunch.
Ask locals where the best beaches are and go there. There is some FANTASTIC snorkeling and diving so make sure to try. On Moorea we rented a car for the day and stopped at a very small, rocky beach that had some local families swimming there. It didn't look like much but it was one of the best snorkeling experiences I've ever had anywhere. BTW: Topless is normal for the beaches so don't be offended.
You will think 10 days isn't long enough.
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