I don't think any of them were spiritual in the way we think of the word spiritual. Remember, these people are only one and two generations removed from the original discovery by Abraham that there exists a God; a God named I AM. I don't see this concept of God's identity absorbed into their beings. They live in a polytheistic culture that worships capricious gods, and I think they treat the "God of Abraham" the same way, perhaps not realizing what they are doing.
Rebekah-- who, unlike Isaac, was not the daughter of someone who knew and worshipped "the God of Abraham"-- clearly expects God to be able to answer her question, and intuits that the jostling of her sons means more than merely "boy, those are active little babies". However, she is manipulative and flippant. She never expresses a desire to please or to worship God, only to extract prophetic information from him. At one point she says to Jacob something along the lines of "If Isaac is going to curse you, fine, let the curse fall on me". On top of that, she was racist, and complains bitterly about Esau's Hittite wives. You could argue that this was centuries ago, when racism was not an issue in the minds and the hearts of the people, but it seems nonetheless that Rebekah's intolerance of the Hittite women exceeds that of anyone else.
Isaac-- I see him as someone dreamy, gullible, passive, submissive. He sees injustice happening before his eyes, (e.g. the stew incident), and does not even protest, let alone refuse to take part. Perhaps he would have been able to take back the blessing, but it is just not in his character to do so. The same character of submissiveness is shown in his response to the people who kept trying to take over his wells. Maybe this is the inevitable character of one nearly slaughtered by his own father in an act of sacrifice? In the end, people like him, and he responds favorably to their requests to live peacefully with him. He is sensuous, and vulnerable. He loves Esau on a deep, emotional level; a level evoked by the smell of the outdoors on the ruse-garment worn by Jacob. I don't see the same genuine feeling between Rebekah and Jacob. I like Isaac. I think he is the closest thing to what we think of as spiritual.
Jacob-- I think he is one of my least favorite Bible characters ever. I mean, he is compelling, and that's why I am here, studying his story. But I can't stand the man. There is not one ounce of reverence in his body. Notice even the way he refers to God-- he calls God "the Lord YOUR God" to his father. He professes no relationship with God, of his own. The experience with the dream of the ladder totally takes him by surprise. Even then, he is not moved to submission by the mere presence of God. He strikes a deal. An if-then deal! He says something like "God, first you have to take care of me etc, and THEN, you will be my God."
Esau-- I have trouble wrapping my head around him. His actions are beyond unwise-- they make no sense! Maybe there was something wrong with him-- maybe he had a cognitive disability of some sort. Otherwise, how would he have brought himself to selling his birthright for a bowl of stew? (And how would Jacob have even thought to ask him?) If this is the case, I can't judge him for making bad decisions, and it makes me despise Jacob all the more.