If you are from the UK you will almost certainly not get the best exchange rate using your debit card at ATM's if you you have a debit card from one of what we call "the high street banks".
My bank, NatWest, part of the massive Royal Bank of Scotland group now charges a 2% "Foreign Currency Withdrawal Charge plus a 2.75% "Exchange Rate Transaction Fee". Other high street banks have very similar charges.
A while ago there were a few accounts available e.g. Nationwide, that had no charges for foreign use. I am not aware of any that are still available to new applicants.
The mantra that withdrawing cash from ATM's is always the best way to go is simply wrong for most UK travellers.
Using todays exchange rates ATMs would give me a euro rate of 1.0910, whereas the Post Office are offering 1.1132 and Travelex 1.12 ( if ordered a day in advance and collected at the airport.
I still use ATM's abroad because they are convenient and can save carrying large amounts of cash but please stop telling UK travellers that ATMs are cheapest....they are not!