What is the best form of money to bring to Cuba?

At this time, the best form of money is CASH. US credit cards are not accepted and it is difficult to obtain money if you run out of cash.

Once there, you must exchange your American dollars for Cuban CUCs.  The exchange rate is the same everywhere:  13% for U.S. dollars.  You will be able to convert your money at the hotel you are staying in as well as at the airport.  If you already have Euros or any other currency, you may bring that to convert to CUCs.  However, it is not going to save you money to exchange your USD to another currency and then to CUC.