What is the best way to change money in Europe?

ATM is best, as was said, but be sure, that if you have letters in your PIN, to memorize what number goes with them, as many ATMs in Europe do not have letters on the keypad. Also, make sure your ATM takes out of checking, as most ATMs in Europe do not let you choose which account, and you might ask your home bank to raise your limit, as well as let them know that you will be withdrawing more than usual, so as not to alert the fraud department. It is better to take out all that you think you will use, as your home bank will charge a fee on the transaction, but it is generally a per transaction fee, so you will save money in the long run.
It is advisable to take some cash money as well, and the AAA can sell you a "trippak" of about $20? worth or Euros to get you started.

Go to a bar that accepts american dollars, buy some drinks, and pay with 100 dollar bills, theyll give you euro's instead

The best rates are from credit card, if you can pay that way, even with the 2% fees. The next best way is from an ATM machine, especially with larger quantities. There are also AMEX offices scattered around that will change money.

I don't know the best,but the safe is at the bank or exchange office!!!

Any bank will change for you. Also the airport, but the rate won't be as good.
You can also check with your local back. If they may have enough on hand, if not they can order the Euros for you.

banks, toll booths, & your embassy

Well, if you're not in europe yet, at the airport, but if you are, the banks are better. They go by the daily exchange rate.

like in US
go to a bank

Are you Iranian?

no, the airport....

trust me.

i converted european money to american from other places and they look alot of interest in it. more than the airport so do it there.

As another person mentioned, it may be more economical to do it with a credit card, but it is difficult to do outside of the major train stations or airports. Most local banks do not like to do business if you do not have an account with them. ATM is definitely the easiest and can be found most everywhere around Europe. I have never seen one without an option to work in English so it is easy to do as well.

I am guessing you are changing dollars to euros or something like that. Just go to the bank, they usually give you the best rate. It's usually pretty easy just to pull money out of the atm, and the bank will handle the money change. If you are in Eastern Europe (Russia, Belarus, etc), sometimes you can find people who do it on the side and give you a better rate than the bank. Be careful though, it's illegal and you could get busted. Also, the people I went through when I was there, they were all mafia people, but I was dating one of their sisters, so they didn't try to screw me.

Find an exchange company called Forex.
Works perfectly, has great rates and is honest.

Here's how I did it when I lived in Germany:

1) Ask your bank at home what sister banks it has. For example, Bank of America has Deutsche Bank as a sister bank.

2) Use only ATMS from the sister bank. You won't be charged any transaction or exchange fees.

At any airport near you. :)

Depends on where you are. generally the best way is to use an ATM with your cash card.
check the prices they charge you with your bank beforehand. usually every bank has got partners all over the world where you get good conditions. the second best would be traveller cheques. If changing cash, you just have to compare the rates. In Germany the best rate without commission you get at the "Volksbank" or postoffices (they charge a commission, but not very high)

Otherwise just compare where you get the best rate. In London you can bargain with the people a bit. usually I got the best results in the exchange ofices between Oxford Circus and Tottenham court Road