I decided to do a mini-experiment with foreign exchange using VISA and Diners Club in Brasil. The VISA is issued by MBNA, which claims to charge only the 1% fee imposed by VISA itself and no further charge. Diners claims a 2% charge on non-US dollar charges. The wholesale exchange rate published in the newspapers for that day was R$ 2.94 to US$ 1.00. The retail tourist rate for cash was R$2.80, or up to R$2.83 for around US$2,000 and perhaps more for higher amounts (no explicit added fee). Here are the results on the credit cards:

MBNA VISA: 2.910
Diners Club: 2.878

The MBNA VISA rate is exactly –1.02% below the published wholesale rate; the Diners rate is –2.109 below published wholesale. The best of the tourist rates for cash offered to me was –3.741 below wholesale.

The MBNA VISA (Motley Fool) has no annual fee and provides a 1% rebate on the total dollar amount; Diners has a $95 annual fee ($35 for additional cards) and an extensive reward program.