So far rule of thumb has been to charge your credit card as much as possible. Using your credit card does avoid converting a lot of cash, however you cannot use the credit card everywhere. Depending on your card,it may still involve exchange fees, but almost always less than retail exchange rates.
The best deal you can get is by using an ATM card. Using the right ATM card will avoid fees and can get the exact exchange rate. Before blindly using your ATM card, check with your credit union or bank as my experience shows not all fine print is the same!
I have an ATM card from Bank of America which is affliated to the "Global ATM Alliance" and have used at International ATMs listed below without getting charged any sort of transaction/bank fees;
- France - BNP Paribas
- England - Barclays
- Germany - Deutsche Bank
- Australia - Westpac