Head to your bank or credit union before you leave to avoid paying ATM transaction costs. You may even receive a better exchange rate. Credit unions and banks will exchange your dollars into a foreign currency before and after your trip when you have a checking or savings account with them.
Is it better to transfer in USD or foreign currency?
With fewer intermediary banks involved in local currency wire transactions, wires typically take less time to process and arrive sooner than wires sent in USD. Fewer fees.
Is it better to convert dollars to euros in Europe or US?
With time at your disposal, you'll be able to see exactly what the fee and rate is, and how many euros you'll get for your dollars. It's possible of course that you might get a better deal when you land in Europe. It may well be the case that fees are lower and exchange rates better.