What's better when traveling, use your credit card to get cash or use your bank debit card?

Going to England and then Paris to visit friends. I can use a credit card for purchases; but how do you know which ATM’s are going to rip you off, percentage-wise? I’m not going to spend that much money; maybe it doesn’t matter that much. But I don’t want to do something idiotic and be mad at myself later. Please advise.