Disagree with anyone who says to miss Tahiti. Tahiti is somewhat different to Rarotonga. While Rarotonga is a very quiet, unspoiled place, Tahiti has been a bit more populated (nothing like Hawaii, though), and there is definitely a bit more happening. It is always interesting to experience the French culture in the South Pacific, as well as the cuisine. Moorea, the neighbouring Island, is beautiful, and a lot quieter. The rest of the Society Islands, and in particular Bora Bora, are very beautiful. I don't know for myself about the other Island groups in French Polynesia, such as the Marquesias, but I am told that they are different to the others, and beautiful in their own ways.
So, it is really up to you and how much you are wanting to spend. If you are only going for one destination, then do a bit of research, and choose whichever you prefer. If you are doing more than one, then definitely try both Rarotonga and Tahiti (and try and get to Aitutaki and Bora Bora respectively if it is within your budget).
One final suggestion - try going during the northern hemisphere summer, as this is the dry season. When I was in French Polynesia, it was December, and we got a fair amount of rain. Most travel brochures should advise the best time of year to go (in terms of climate and price).
Here are some websites you may find useful:
- Air Rarotonga (the inter-island airline in the Cooks)
- Air Tahiti (The inter-island airline in French Polynesia)
- Cook Islands Tourism Corporation (Check out the accommodation; websites aren't given, but try the domain names from the e-mail addresses they give)
- Air New Zealand's schedule to RAR, from the above site.
- North American site for Tahiti Tourisme
- Tahiti Tourisme's International Site
Regarding Air New Zealand, yes they are two class flights, on the 767-300. I would highly recommend Air New Zealand's Business Class. It doesn't have all the wizzbang electronics of, say, Singapore or Cathay, but the seat is very comfortable, you get a 12 channel PTV, and the service I have found to always be top-notch. If you do a search on the internet, I think you will find the vast majority of reviews are very positive. Here is what Air NZ's website has about Business Class: http://www.airnz.co.nz/nz/ontheplane/business_class.htm
Hope this is useful for you, look forward to hearing more about your trip