Dolphins in their natural habitat, are more likely to be seen from the boat.

The few times I've been in the water diving when they're around, they might look on, but they always take off. They have a quick look and go.

The habits of flipper were trained animals, not wild.

I'd say the north side of Tortola or the SFD channel have offered the most frequent sightings for me. And the sail to St Maarten.