Bora Bora is actually very small and if you're going there, it's more about the resort you are staying at and what things they have to do or see (or using a boat to get from resort to resort). The actual little built up area of Bora Bora can be walked in about 15 minutes. Bora Bora has that "it's so perfectly beautiful that you wonder if Disney animatronics didn't have a hand in it" thing going on.

Moorea is more built up. We kayaked, hiked, rented a car and visited local markets, Little villages with churches and town centers, etc.

Both places are geared toward relaxing, snorkeling, swimming, kayaking, and eating. The over the water bungalow with the glass floor/plunge pool/steps into the water setup both places are known for is amazing.

Lots of reef sharks. Avoid swimming during dusk and dawn when they come close to eat. Although I doubt they'd eat you, it's a little alarming.

Do you know where you're staying? We stayed at the same place both trips to Moorea and we were very happy with it. The resort we chose on Bora Bora was absolutely beautiful.