My first trip to IRL (1971)I used US AmEx checks and paid to convert. While in Ireland learned English pounds and Irish punts exchanged equally. I wised up. There was an Barclay's Bank (of UK) in Boston, so I went there and bought travel checks in pounds for later trips to UK and IRL. Sure, paid for checks, but just once, not at every exchange.
Haven't had any experience with Euros.
What are your experiences with credit cards. One chum of mine was very upset when charges were held a long time to get besxt exchange rate for the stores!