We're travelling to London and Paris next week from the US -- looking at having prepaid debit cards for spending money instead of carrying a lot of cash. Is there a preferred card in these cities?
Discover Card has very limited acceptance outside of the United States. Indeed, since it's almost strictly issued in the U.S. only, most people abroad have no clue what it is.
In Europe, it is only accepted in a few countries, of which France is not one. If you do end up in one of the countries where it is accepted, remember to indicate that it should be run as a Diners Club card.