Norman is first choice if you get away late from the dock. There are about 4 balls at Water point and if you can get one you will be rewarded with some pretty nice snorkeling from your boat. There are some really nice underwater cliffs and crevices with lots of nice coral and fish of course. Then in the morning you would be well set up to visit the Indians or the Caves at at Privateer Bay.
But if you do get away early enough I would suggest Cooper (weather permitting of course). Cistern Point is a favorite place to snorkel and the resort on the island is pretty nice as well. Good food and service, a really cool Rum Bar, nice beach and a laid back vibe. If Cooper is out of mooring balls or if it is too rolly when you get there I would head across to Marina Cay. We haven't been there in quite a few years so someone else will have to chime in about all it has to offer these days. Have fun!