Depends what you like, and how badly you want to snorkel.

The outrigger canoe and 4x4 tour is very good, I've taken it twice. You see one of the ancient sites, get a ride through the hills and valleys of plantations, and get a boat ride up the only navigable river in FP.

There's also a really swell sail, if you happen to be sailors, but it's quite pricey, my husband took it.

I did the circle-island boat ride with snorkel recently. The boat takes you all the way around the island, which is pretty long, so you have to like riding in a boat. There's about a half hour of really good snorkelling halfway out.