Effective 05/01 the Delta American Express cards will no longer charge a foreign transaction fee and will have a chip to make spending abroad easier.
It’s can be worth getting the card for the signup bonus and having the card for the benefits. Those include a free checked bag for you and 8 other travel companions and getting to board early which can be the difference between having space for your carry-on or having to check it to your destination. The Delta Platinum and Reserve cards also give a free annual companion ticket.
However it’s generally not worth spending on Delta cards as Skymiles are one of the worst mileage currencies out there. (I say generally because the Delta Platinum and Reserve cards can earn elite qualifying miles based on spending. Plus if you spend $25K on any Delta card you can earn elite status for 2014 even without spending the new required flight spending amounts on top of required flown miles) But even if you do want Skymiles (there are some decent uses such a business class to Tahiti or Australia or getting a free stopover within the US) you can earn them faster on the Starwood Preferred Guest® Credit Card from American Express as 20K Starpoints transfers into 25K Delta Skymiles.
The points earned from the American Express® Premier Rewards Gold Card transfer to Delta as well and that card earns 3 points per dollar on airfare (as well as 2 points per dollar on gas and groceries and a 15K annual bonus for spending $30K).
Of course both of those cards charge foreign transaction fees. Hopefully that will change soon, but in the meantime if you want miles the best cards to use abroad with no foreign transaction fees include the Chase Sapphire Preferred , Ink Plus , and Ink Bold. The Sapphire card earns 1.07-3.21 points per dollar and the Ink cards earn up to 5 points per dollar and those points can be transferred to several airlines and hotels, though not to Delta.