Bond is out early in my mind. He's used to dominating. Put him against real competition in his own field and he'll be screwed by being careless.
Hunt is probably the superior spy and can set some good trap for the other 2.
But I think Bourne will be the winner as the survivor. Ethan will probably get him in a good trap and want to question him. Giving Borne the opportunity to escape and turn it into a direct conflict where he will come out on top.
Borne high difficulty