Are you doing the Med cruise or the Baltic? In the Baltic area, euros will not help you for 2/3 of the countries. As for the credit card, I've heard that using it to get money from an ATM can often incur serious charges, so I'd double check with your CC company before going that route.
ETA - Ah, I see September, so that's probably the Med. Make sure your CC has a chip with a PIN.
We use our debit card at ATM's all over the world. We did change some money on the ship.