It would be too difficult for me to speculate on where they may go, although I think JFK is a dead cert...in fact, I think a trip to Ladbrokes is in order on that one.
They will have to be very careful indeed though, because a lot of airlines are going to open up new LHR-USA routes and the competition will be fierce, there will be a price war, and it could get very ugly very fast for some of the airlines involved.