Earl Harold is a fine specimen of a warrior: tall, handsome, in the prime of his physical powers, and intelligent as well. You warm to him, but hide your feelings well: it won't do to become friends with your greatest rival in England. You need him to work for you. But he is most contrary, preferring to act ignorant and ineffective, each time you bring up the subject of what he could do for you, to help make you king there; and what you would do for him in return for services rendered. He seems eager to please, and at the same time, unwilling to do anything (commit to anything) to further your ambition. Your patience is sorely tried. What, after all, is the best thng to do with this important English magnate? He could be so very helpful to your cause, and yet he could be your worst enemy.
You decide the safest thing is to simply execute Harold.
You could knight him instead, and exchange oaths of fealty.
Keep Harold in Normandy for life.
Ransom Harold back to king Edward and send him home.