When I do dislike one character more than the other it's usually as you said that in canon it isn't written well AND I still like the dynamic between the two characters because then one I love helps make the one I don't like as much better.

I agree with you about Rodney. Usually too I see him being an ass as not serious or more done in a joking manner rather than something that he means seriously or as you pointed out, is not looked badly upon by others and not treated as something bad.