Originally Posted by
Some person
AMEX has a higher exchange rate markup than most other cards (if paying in foreign currency), so it's better to use some other card.
This is definitely a YMMV thing. In fact, there are lots of reports in
this thread about Visa having worse exchange rates than both AmEx and MC. The possible ~0.5-1% difference is still going to be better than anything DCC offers in any case.