It really depends on what you mean by cheapest, and on what type of consumer you are.

Let's say you fit into one of two groups: you are someone who pays off their balance in full each month, or you're not.

If you pay your balance, you should opt for a card with a low annual fee and a good interest free period (e.g. 55 days). The purchase rate is less important if you're this kind of consumer, as your balances will probably never get to the stage of accruing interest.

If, like most people, you don't pay your balance in full each month, purchase rate is key. Go for a card with a low rate (less than 11%) and if you can, a good interest free period.

The NAB Low Rate Visa, Citibank Clear Platinum, Aussie MasterCard, Bankwest Lite MasterCard and Vertigo MasterCard are all good options.

Use our comparison table and sort by the 'Interest rate (purchases)' column to see the cards with the best purchase rate.

In your page comparing credit cards you showed comparisons of their Overseas Transaction Fee and Overseas Cash Advance Fee.

That was useful but the banks also differ in the exchange rates they use when converting foreign currency transactions to the currency of the card. Presumably, a bank could have low fees but use an uncompetitive exchange rate, or vice versa!

Yep, that's true.

Unfortunately, because exchange rates change so often, it's difficult to provide a good static comparison.

I don't know how much variance there is in the exchange rates offered by different banks, but it would be an interesting study. I might look into it.

Thanks for the comment.

I've just put up an article which compares the foreign exchange rates of nine Australian banks.

It won't be updated regularly, but it gives an indication of just how much difference the FX rate can make.

Thanks for your contribution Jack.