You will not find an ATM which dispenses USD on St Barth, only those which dispense Euros. As to fees, it's going to depend on your bank and the fees which they charge or pass through more than anything else. That being said, I prefer the BNP Paribas ATM in Gustavia. Being the only "inside" ATM which I've found, I've always thought of it as being marginally safer from skimmers than other ATMs. In the days of chip-and-PIN cards that may no longer be a concern, but I pre-date chip-and-PIN and old habits die hard.