Cards are usually pretty convenient and safer than carrying lots of cash - but many travellers prefer to have both cards and a small amount of cash to hand. When it comes to cost, which is best depends on the exchange rates you can get for your specific currency pair.
If you have a card which doesn’t charge a foreign transaction or foreign cash fee you’ll usually find that the exchange rates set by card issuers and used when you spend and withdraw are pretty fair. Choose a specialist travel card which offers the Google exchange rate to get even better value.