the post office card has no FX fees, and you'll get a good rate of exchange too. Also, no annual fee. their website gives a reply within 6 days if you want to take a credit card.
Debit cards are sound if used shrewdly.
bearing in mind almost all ATM's will charge you a fee (nothing to do with your bank) of around 1.5%, or a minimum of �1.50........use it 5 times on holiday, and withdraw say, �100 each time, and you could be looking at fees of �7.50 - �20 (inc bank charges).
so, sometimes, TC's are worth taking.