I would go with an Eide Mar denari. Minted by Brutus to celebrate his assassination of Caesar, I guess he didn't know how unpopular that act really was while he was celebrating. Second pick would be the silver coin with Mark Antony on one side, and Cleopatra VII on the other struck shortly before Actium. On that coin Cleopatra is described as a living goddess, while Antony just a "successful general". I guess we know who wore the pants in that relationship! A third pick would be a Kimon signed Syracuse coin, arguably the finest ancient coin ever minted. This all depends on WHY I would want the coin. These choices would be for my own personal satisfaction, or course if I simply was free to sell one coin I would choose the most valuable one, probably either the 1933 double eagle or the 1849 double eagle. Sell that and buy all three of my picks!
How about one of the missing gold Libertas Americana Medals which were given to King Louis XVI and Queen Marie Antoinette of France? GatewayCoinGuy
I would like to own a controversial coin , so it would have to be either: 1.) 1849 Twenty-Five Dollars California Gold (minted by Templeton Reid). The reason for wanting this coin is because it was the only known example and was stolen from the U.S.Mint in 1858 and never recovered. This according to the 2011 RedBook. or 2.) The 1974 Aluminum U.S. Cent (never allowed into circulation).