I agree with Badbenni. The guilders that are used here on Dutch Sint Maarten really aren't a good value and take second tier to the U.S. Dollar IMO. They're kind of a local currency that's still hanging around, and not flexible to use like the euro which you can use throughout most of continental Europe if and when you go there. As for euros on the French side, that's up to you but I found it's always helpful to have some with you based on the currency exchange rates being used by the establishments you visit. As of today, one euro is equal to $1.11 USD. So, it's smart to do the math if they accept both euros and dollars. But, it's really good when places on the French side show an even one-on-one exchange rate between euros and dollars. Also, one U.S. Dollar is worth roughly 1.78 Netherlands Guilder if that helps.