osprey:The Abacos are very nice, but poor diving. Like they already said Harbor Island has the only diving operation on Eleuthera. Castaway Cay is for cruise ship passengers only. There is no air service or dive operators in the Berries. For what you describe I would try Small Hope Bay on Andros or Riding Rock Inn on San Salvador.
I think the Abacos are great, if you don't mind shallow diving. Fowl Cay preserve is beautiful, but you will have a hard time finding more than 50' at the outer edge. I have been there many times, and my favorite thing to do is fly into Marsh Harbor, rent a boat at Boat Harbor Marina (the name of the outfit escapes me, but I can find out) and stay in Hopetown. Froggies is a good little dive outfit right in the harbor at hopetown. If you are comfortable boating, it is no problem to get out to the reefs on your own. Rent the Albury 20 or 23, they are great little boats and built across the sound on Man 'o' War Cay. Another good dive outfit is on the main harbor at Marsh Harbor, owner's name is Keith.
PM me for more specific info. Renting a boat, even if you don't dive from it is the way to go. Head south in the sound to Tahiti beach at Tilloo cut on the end of Elbow Cay for one of the prettiest beaches in the world. Further south down Tilloo Cay, you will find other pristine beaches as well as a nice reef in the abaco sound that is a preserve as well with mooring buoys for diving in 25' depths. Again, the name of that reef escapes me, but I can look at my notes.
One bit of advice. You will be labeled as a novice visitor to the Abacos if you pronounce the "keys" as they are spelled "cays".
Another thing, 3 days is not nearly enough. It is my favorite place in the world.