I like them about equal.
Strangely, the thing I like about Carver is his constant desire and moaning to be his own man and to get out of his brother's shadow, but I get the feeling that he puts himself into his brother's shadow because his sense of duty to his family is so strong that he can't help but act in line with it. Well, I kind of got that impression in a dialogue with Varic where Carver goes out of his way to let Varric know he's not interested in being the star of any of his stories, and then gets jealous when Varric says he's not worth making the main attraction.
He wants things one way, and gripes about it when he's being told he's getting it. He seems to live to complain because he doesn't know what else to do. I know if I knew him in real life I would probably get annoyed really fast, especially that he's never seems satisfied with anything, he has to whine about every situation they end up in. But I love the dynamic he offers to Hawke and how he develops as a Warden or a Templar.
My Hawke left Carver behind because he wanted a few weeks of peace without hearing him whine about every little thing or every decision Hawke makes.
I love how sarcastic Bethany can be, I love her attitude, her sunny disposition gives my Hawke something worth fighting for and I was surprised at how vindictive she can be as a Warden, although I shouldn't have been since I saw elements of that side of her when it comes to Gamlen. She is a loving person, and is far more willing to see the brighter side of things than Carver, who could only focus on the negative.
I can see why some people would prefer one over the other, they are polar opposites in personality, but I love the relationship my Hawke can have with both.