Best way to make international purchases

I'm trying to determine this right now. I called two of my credit card companies and they both charge a 3% fee and a mystery exchange rate. To withdraw funds from a non-US ATM, there is a $3.00 charge. I'll probably go to the bank before I go and buy some Euros here, so at least some of my purchases won't have a surcharge. I hate this. Any method feels so non-transparent.