Amex has very high exchange rates, visa mastercard I much better in this sense. but if Dan say a SPG could be worth $0.05, then he can use it, o/w I'd switch.
The last couple of month, they wrote on my only bill how much the the difference was between their rates and the actual conversions.
As the sums involved were pretty decent ones, I paid often well over $300-500 just in amex charges for single transactions.
this hurts....