Today I used both credit cards, the Chase Presidential Plus (discontinued), and the Capital One Venture card.
The first charges were at the gas station and the office supply store on the Chase card (business expenses). Chase is the card that doesn't apply the exchange rate until the time of processing, which is usually the next day. This can work for or against you.
Today's best street rate at the local money exchange booths was 36.24 baht/USD.
The rate I received at Chase (processed one day later on the 7th) was: 36.09 baht/USD. The more I monitor this Chase MasterCard, the more I notice slightly worse rates than the local exchange. HOWEVER, had the rates increased in my favor the next day, I would have benefited. In most cases however, I have not. I also do not know if Chase Visa's have a better rate.
On the Capital One Card, the rate I received was: 36.20 baht/USD. A better rate than I received with Chase but still below local exchange rates.
In a matter of speaking, I "lost" 22-cents on each card. Although I had to see a negative, I accept the loss instead of having to pay everything with cash.
But I really didn't lose anything! With Chase, I earned United miles. At the "standard" valuation of 2-cents per mile, I earned $1.06 in miles. Because of the way I redeem my miles, I get 5-6 cents per mile, meaning I did MUCH better than the $1.06!
With Capital One, I earned $5.66 in reward points, that I will use to "erase" travel expenses such as hotels and meals eaten at hotels.
When you look at the whole picture, I didn't lose.