Here's my thoughts, Cabel seems to help her in the most critical moments. The time where her divine powers could not come out, saving her when she was not reacting, cheering her up in a blunt way.
Elvin, on the other hand, I think he uses words instead of actions, he healed her once, but Cabel is the one doing the most saving.
Cabel is more transparent in certain regards, while Elvin is more subtle.
Subjective part: I think Cabel does a better job at being someone reliable and someone Renee needs, he's my favorite as of now unless he suddenly becomes violent, I think he has the best chances in the long run.
Also, is It me or is the prince hiding something dark?