What's the difference? Neither is subject to MQDs. Neither will work if your flying is done mostly in the US, should DL audit your account. Tickets are priced in the currency of the place of origin of the itinerary and subject to the published fares ex- the destination city. The only difference I can see would be that you might get (or not get) different promotional offers. And the credit cards available to you. There are Citibank Visa cards in HK with which you can earn DL miles, but the conversion rate is poor and there are much better cards out there.