Many years ago, one could use AAA to buy pounds, French francs, Swiss francs, Dutch guilders, and German marks denominated travellers checks at very good rates and as an AAA member without fees. The problem was in using them in Europe, as few merchants in these countries take them. One had to find the Amex office to cash them in, again without fee. After the euro came out, I tried this again, but the exchange rate was terrible. I have checked once since with the same result. In the old days, this was a good way to lock in an exchange rate when the dollar was on an upward path, but it does not seem to work any more.
The local banks I have checked rates with in North Carolina in the past give awful exchange rates, and it would be poor value to change money ahead of time with them.
Having money on hand when I arrive has never been a problem. In the UK, when I arrive at Gatwick, I use plastic (CapOne) to buy a rail ticket to Victoria Station, then walk outside the station across the street to a currency exchange office that always has great rates and no commission and change cash there. The exchange offices inside the station are another matter, as they have bad rates, high commissions, or both.
If you really need money at the airport, you can usually find exchange offices with bad rates and/or high commissions at most European airports (Zurich is an exception - good rates in both terminals and no commision in one of them). There are usually ATM's but beware of machine owner fees on these. Also almost all airport shops, including fast foods will take dollars and give change in local currency, usually at not that great a rate but at least without a commission. This can be an option for small amounts of local currency. Airport exchange offices in US airports offer bad rates and/or high commissions.
In the UK, many bank ATM's do not charge a machine owner fee, and they usually tell you that on the screen. Elsewhere in Europe that may be a crap shoot unless you use a guidebook that tells you which banks charge what on ATM's. In Greece, for example, all bank ATM's do charge a user fee on ATM's but they vary, so you need to look out of the banks with the lowest fees.
The other thing to watch out for with ATM's is the fee that your bank charges. They do this two ways, a percentage plus a flat fee per use. The per use charge at my two Credit Union accounts is 75 cents and the percentage charge is 1 percent. The bank I still use, but will probably close out, charges $3 flat fee per usage plus 3%.
Are ATM's the best? Not here in eastern Europe. Exchange offices here almost never charge a commission, and rates are great. I can often change currencies at within one half of a percent of the mid-market interbank rate, and occasionally even get a better rate than the interbank rate. Sometimes even a double conversion offers a better deal at exchange houses here than ATM's. Recently I needed some Swiss francs to pay a bill in Switzerland but was not going to be travelling there. In converting dollars (the currency I am paid in) to local currency, I got a rate within a bit less than half a percent of mid-market interbank rate, and when I went to convert that local currency to Swiss francs, I got a rate almost a full percentage point BETTER than the midmarket interbank rate. So on that double conversion, using exchange offices, I came out almost half a point better, on net, than the interbank mid-market rate. The same is no longer true in most of western Europe. Since the euro came in, the rates at the exchange offices have gotten much worse than in the days of national currencies.
"They" say that the best way to obtain foreign currency is by using ATM's in the country you are in.
However, I like to arrive with enuff local currency in my pocket to hit the ground running. Most suppliers build their commission and credit card fees into their exchange rate, which can differ significantly. So check with a number of different sources (including your bank). I just checked these. I input 670 GBP for each and obtained the quotes in parentheses (including delivery).
Wells Fargo Foreign Currency:
https://www.foreignexchangeservices.com/ ($967)
Oanda FX Delivery:
http://www.oanda.com/products/fxdelivery/ ($1020)
Int'l. Currency Express:
http://www1.foreignmoney.com/ ($1,041)
Travelex Foreign Currency:
http://www.travelex.com/us/ ($1042)
Wells Fargo has consistently given me the best results, but I'd be interested to hear what other sources folks have used.
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From a SNL skit by Eric Idle:
"You know, there's one thing we English have always loved above all of you Americans, and that is... your money. We have a thousand-year history... you have the money. We have the literature, the poetry, the traditions... you have the money. We have the buildings, the paintings, the gardens, the palaces... you have the money. And that's why we are here tonigt. We are going to hold a telethon for England. If you wish to plesdge money for England, an ancient charity, here is the number to ring: 555-1066."