I can't vouch for either place but you may want to pick the closest to you and exchange a few hundred USD to get you by until you get a better handle on the exchange rate. I'm always amazed by the huge wad of J-bucks I walk out with. Also some ATMs allow you to access your bank account with your debit card and choose USD or J-bucks for withdrawal. Fees vary from ATM to ATM but it's usually a few bucks as I recall and I'm willing to pay for the convenience.