I don't think an F-16 would be too great; it would compete with the another company F16.  Also, from what I've seen, people like to see aircraft from Captain Sim that have been neglected by the developers, like the C130.  Other fighters, perhaps some of the great Russian ones, would do well, especially if they modeled the canards, thrust vectoring, etc.  Like the C130, I think the BUFF will sell better than, say, the 757, as it's less common.