The answer is a combination of most--but not all--of those methods. From what I have gathered in my research, I'd advise the following:
1) Take some US dollars to use for tips, snacks and purchases in the airport from which you are departing. In addition, take enough extra cash so that you have $20 to $30 per day for each day of your cruise--10 days, $200 to $300, for example--to convert to the local currencies of the cities you will be visiting, just for small purchases from street vendors and local shops that do not take charge cards, tips, snacks, etc. Pickpockets can be a problem in Europe, especially in the big cities; so keep all but about $30.00-$50.00 in the safe in your cruise stateroom. What you do carry with you, keep in a money belt, preferably one that you wear around your neck.
2) Take perhaps $300 in travelers checks, just in case of an emergency. Chances are good that you will take them back home and deposit them in your checking account. Currency exchangers charge the highest fees when making exchanges for travelers checks.
3) ATM's offer the best rates for currency exchanges. There are numerous ATM's in most major cities in Europe--a little harder to find in small towns. Check with your bank to make certain that your ATM card will work on European ATM's--not all do! When you get to each country, exchange enough currency so that you have $20 to $30 per day for each day you will be there. As mentioned above, this will be used for tips, small purchases in local shops that do not take charge cards, etc.
4) MasterCard, Visa, American Express, and Diners ClubCharge cards are acceptable in many restaurants and shops and in most department stores. While credit cards are very convenient, your bank may charge a fee for converting charges from European currency to US dollars. Call to inquire. Citibank was charging 3% last time I checked. Not all banks have this policy, and it may pay to open an account with a bank that has no such fee just for your upcoming cruise.
5) There is no need for money orders. Fees for currency conversion are high.
One more tip: If you are going to be travelling to many countries, each of which has its own currency, you might want to take some currency "cheat sheets" with you, as provided at Oanada's website:
The exchange rate varies slightly from day to day, but if you print out the exchange rates for various foreign currency you will be needing, you will have a good idea of what rates to expect.