In general the US programs (so US and UA) are the most generous with earning mileage. They have the fewest excluded fares or fares that earn only a percentage of miles flown in some of the lower booking classes. Maybe you can sign up for both of them and then when you figure out the class of the ticket (if it is after the flight), you can decide which program to credit to. Make sure you save your boarding pass so you can send it in.

If you know beforehand, then just check all the websites of the various *A FFPs until you find one that will give credit for the fare class. Start with UA and US and try LH, Aegean, AC, Asiana (I think miles earned with them are good for seven years), etc.