Do Europe's ATMs offer good US$ → € exchange rates, or would I get a better rate buying € in the U.S. at a bank?
Typically, there is a series of fees associated, and you often only see the total, so it is hard to compare.
- the owner of the ATM might charge a fee
- the owner of the location might charge a fee
- the company maintaining (restocking) the ATM might charge a fee
- the bank whos name is on it might take a fee
- your bank might take a fee
- any intermediate bank that connects your bank with the bank in the foreign country might take a fee
- one of the 2+ banks does the actual currency conversion, and although they typically use the interbank exchange rate, they add a fee too; typically as a percentage
As said, some of the fees are 'merged' into the rate, so you don't see them (and there is a little sticker on the ATM [probably in 4pt-font and under the bottom of the machine], that informs you about it).
Your best chance is with ATMs inside banks, with large international bank, or ATMs from banks associated with your bank; that removes many of the potential fees.
Buying currency is not that cheap either, because it requires for a US bank to have Euros, or for a European bank to have US dollar; both of which is effort and they will therefore take a fee, oftne rather higher than ATMs.
Worst possibility is exchanging in the airport (most convenient = most expensive).
Your best choice is to pay as much as possible with credit card; many offer real fee-free conversion. For the cash you absolutely need, ATMs are the least expensive, as said, stick with ATMs inside banks if you have a choice.
In the EU, the Payment Services Directive 2, article 3(o), which went into force in January 2018, requires that ATMs inform you of every fee and charge added by the ATM operator before you make the withdrawal.
As Aganju says, free-standing ATMs are generally more likely to charge additional fees than ATMs at bank branches.
Usually the withdrawn amount will be reported in the currency you actually get and your card issuer will convert it to your currency according to their own rules. Card issuers often add various fees to out-of-country cash withdrawals, but that is independent of the ATM being in Europe specifically. Familiarize yourself with your card issuer's conditions before traveling. If you have multiple cards, it is possible that the one that is cheapest to use at home is not the one that is cheapest to use abroad. (And this may differ between use in stores and ATMs).
Some ATMs offer to do the currency conversion for you and charge your card in your own currency. This uses exchange rates set by the ATM operators. The rates will usually be worse than what your card issuer would use. The Directive requires that the ATM must show the exchange rate (and any other fees connected with this feature) before you choose to use it. Unfortunately it's not easy to check your issuer's current rates while you're standing at the ATM, but if you remember their latest published rates you will at least have a fighting chance of judging whether you're being offered a bargain or a scam.
Unless you hit a particularly greedy ATM operator, withdrawing local currency at an ATM will almost always be cheaper than exchanging cash from home. Getting physical euro notes transported to your home country just so you can carry them back to Europe costs money, and those costs will be borne by you in the form of worse exchange rates than electronic transactions carry.
In addition to the other responses, there’s one thing to consider: some banis have an international presence, others have international partners. Those banks will usually offer reduced fees at their own / their partners’ ATMs, so check if this is the case before you leave.
In some cases this has very limited use (e.g. Citibank has presence in many countries, but it’s often quite limited so you really need to get out of your way to find one of their ATMs), others have a very large international presence in many countries (e.g HSBC).
Partnerships are a lot let obvious and can sometimes be very useful.
All in all: do you homework before you leave, check your bank(s) and/or card issuer(s) rates and fees.