Marco Island, Key Biscayne, Miami Beach would be my preferences. It has been a while since I have been there but the North Palm Beach to Vero Beach stretch used to be cool. Juno Beach was a hidden jem.
You never said what price range you were looking for. The quandary is the international feel and panache are on the east coast like Palm Beach and Miami but the better beaches and laid back attitude is on the west coast and panhandle.