If St. Maarten becomes an option for you, the diving is not bad IMO. Some nice wrecks (one was a very nice swim through) around Simpson Bay and some nice sites around Great Bay. Reef Sharks were pretty common on most dives around Great Bay. Was planning to go to Saba one day on our last planned trip to St. Maarten in Sept/Oct 2017, but that was at the time the hurricanes came through so the trip obviously didn't happen. Besides the ferry to Saba, there is flight that takes ~15 minutes and flies at a low altitude. I was pretty sure I was going to go the ferry route.
There are a few shore dives. The only one I did (I actually entered from a boat) was in Little Bay. A bunch of junk in a protected marine park at a 20-30 foot depth. It was okay.
Topside, there is a lot of sightseeing, beaches, catamaran sailing, jet skis/tours, and ATV tours. I think they have zip lining and a lazy river type of attraction that is not in water. We did a catamaran tour around the island and made a stop at a small French-side island. We snorkeled, swam, and enjoyed the beach. As we were loading up, another catamaran pulled in next to us - they were doing all of the same activities we had done......but were nude! A catamaran tour from the French side of the island.