I use the Halifax Clarity credit card all the time, there are no charges for using the ATM.
The only cost is the interest which is about 1% a month, so if you pay it off 2 weeks later it will cost 50p per £100. changing cash in the resort will cost 2% (ie £2 per £100) and at a lower exchange rate. Martin Lewis (moneysavingexpert.com) says it the best way to get your Euros.
Also you are not carrying large amounts of cash around, just get what you need.
Don't use any other credit card or debit card as it will cost a lot more.
Having said that, with the Greek crisis, don't just rely on the ATM as the banks may turn them off if Greece defaults on its debt payment.