I would say the best activity of the three 'formal' activities was the sailing - we sailed from amelia island to St Mary's, Georgia and had lunch there before sailing back. - We went up the intercoastal waterway and up the St. Mary's River - literally, since it is one of the few rivers in the U.S. which flows to the North.
Fondest memory: We also had a lot of fun with the parasailing - it was a very stable ride and was handled well by the concessioneers. My only regret is that I left my camera on the boat when I went up - it is just a snapshot camera and would have been easy to use from the parachute.
In any case, it was fun even if it was a bit chilly (we had to wade/swim from the hotel beach to the boat - not too far, but when you're wet, you're wet!)