What is the most efficient way of buying foreign currency?

If I want say £100 worth of Euros should I get it from my bank, the post office, the airport, draw the money out from my bank using a foreign cash machine or buy stuff on my Visa card while abroad. Is one cheaper than the other? I'd love to know the most efficient.

Public Comments

1. u shud change it at an airport, its the best value at the bureau de change or summin.
2. Try the Post Office.
3. I alway change it when I get to the country I am visiting
4. seen this looks good