Originally Posted by stvr

Just got back from a big trip to Japan, where we did a lot of A/B/C testing to see which card gives the lowest rates. Here are my results, by day:

6.9
MC — 106.65 JPY/USD
Amex — 106.49 JPY/USD

6.10
MC — 104.31 JPY/USD
Visa — 103.61 JPY/USD

6.11
MC — 106.15 JPY/USD
Amex — 106.64 JPY/USD
Visa — 102.12 JPY/USD

6.12
MC — 105.77 JPY/USD
Amex — 106.15 JPY/USD
Visa — 105.68 JPY/USD

6.14
MC — 105.80 JPY/USD
Amex — 105.47 JPY/USD
Visa — 103.78 JPY/USD

6.15
MC — 103.57 JPY/USD
Amex — 105.62 JPY/USD
Visa — 103.66 JPY/USD

Very pleased with my Amex. Visa threw some dud rates in there. Some of these differences were 2% or larger!