Australian here, I use a credit card for purchases (even though I pay it off in full every month) because of the Frequent Flyer points I earn. I've already used them for one 3-month Round The World trip. Amex cards usually have a ton of other benefits too.

There's also better fraud protection on Credit Cards over debit cards. Debit cards the money is taken from your account immediately, credit cards it's corrected before you have to pay your card bill.