how is that even a contest? Ramsay is a psychopath who likes torture and kill.
on her worst day, Selyse Baratheon is maybe a little bit of a bitch... you might be too if you've had to suffer through 3 stillborn sons, a husband who parades his mistress around in front of the world to see, and who's been forced to pack up and leave home to hang out in the frozen north of all places.
Cersei is a bitch, but at least she has some redeeming features: she loves her kids, even Joffrey despite knowing he was a monster. And she knows she's a bitch.
Roose Bolton is certainly a major a**hole, but, unlike Ramsay, I don't get the feeling that he enjoys torturing and harming others for its own sake
. He basically doesn't give a shit about others, he just wants power and assets, and all that matters are his own interests. Cersei is also somewhat like that. Ramsay is just a sadistic little prick like Joffrey was. And, like Cersei, I think both Ramsay and Roose do know what they are.
Yes, Selyse had stillborns and Stannis' household is, well, to borrow a quote from Gimli in LOTR: "You'd find more cheer in a graveyard".
But shunning her own daughter because of a physical deformation to the point I don't even feel Shireen is safe around her own mother, something even Stannis doesn't do. Or in the beginning of the 4th season I believe she was cheering and chanting as her own brother was being burnt alive with a smile on her face. That's far beyond any excuses. The religious fanaticism that gives rise to this "hollier than thou" attitude and the misguided sense of self-righteousness, that's what really makes me hate her. She shees herself as a deeply spiritual, pious person, as opposed to the horrible person she really is. And I really get the vibe that she's so brainwashed with this R'hllor, that it makes her happy that Stannis is sc*ewing Melisandre. Like trully happy, not just pretending. And as opposed to Cersei, she doesn't have the looks either...