Hammerhead Cocos Islands, Galapagos, and Baja California/Sea of Cortez are supposed to be good. Haven’t been to any of them, so can’t speak for water temperature or difficulty of the dives. I would suggest doing some wreck diving off North Carolina, water is comfortable, vis is usually good, and almost a guarantee for sand tiger sharks. I have done that dive, and it is something I’d lIke to do again.