It really depends upon where you are based.
Moorea is a more stunning island because of its two magnificent bays and those jagged mountains. But the Isle of Pines property has a more stunning location with the most amazing beach and turquoise water you could imagine, and I don't say that lightly because I've been to Bora Bora eight times!
Upgrades at the Moorea property are easier to get, but usually to a beach bungalow. At the IoP property upgrades are from rooms to one side of a duplex bungalow, and they are all much of a muchness: you wouldn't get upgraded to a clifftop one but I can't see why they are viewed as better than the beachside ones anyway.
For me, the real decider is the season, especially as neither property's pool is heated.
For me, New Caledonia is a November, December, January destination: those are the warmest months when it doesn't rain too much.
In contrast, French Polynesia should be avoided at all costs from November to the end of March because it rains all the time.
I don't want Lurker to see this, but the Sheraton Moorea Lagoon is a good property comparable in comfort to a Luxury Collection hotel but with erratic service.
But Le Meridien Isle of Pines ranks alongside the Bora Bora Nui and St Regis Bora Bora as the best Starwood I have ever stayed at, miles better than the St Regis hotels I've stayed at at Monarch Beach and Washington DC.
DCF, can you tell us a bit more about the Le Meridien property as I always thought that the rooms/decor are quite dated. We've been to FP four times and will stay at IC Thalasso in April which is brand new. The bungalow at LM are around $1000 and I was always wondering whether it would be worth it. Are there any bungalows with a nicer view or more privacy at all or maybe closer to the lagoon than others? Are the bungalows duplex bungalows or is there one room per bungalow? From your post I already see that you don't prefer the cliff-top bungalows because they must be further away from the beach.