If you are travelling to major industrialized nations with highly developed financial systems, use your credit card and carry just as much cash as absolutely necessary. Withdraw cash from ATMs using your credit card. When using credit cards for cash withdrawals, it is highly advisable to deposit money into your credit card account prior to your departure in order to avoid the exorbitant interest rates banks charge for cash advances on credit cards. The downside of using foreign ATMs is that you may need to be familiar with the local language, as many do not provide English-language instructions. Ask your credit card issuer about their policies and rates.
Traveler cheques have the advantage that they are insured.
If you lose them they can be replaced. However, in most places where you can use traveler cheques they also accept credit cards. In most industrialized countries credit cards are now more widely accepted than traveler cheques. Using cash is often the most convenient form, but also the most risky. The web offers some very useful starting points as well.