Kevin Johnson would be the best move IMO. Before he would be critisced due to apparently little punching power but he's now on a 3 ko streak against decent boxers in Seldon and Vargas. This has showed a much more aggresive style which makes him more interesting to fans. However its a accumulation of blows, not just one. This would make him god for Haye, plus he's the best/second best US heavyweight (counting the Nightmare as Mexican) and is pretty well known. He needs a big name like Haye on his resume before he can be considered a Klitschko victim.