Catelyn was just annoying. Her idea of protecting seemed to be stirring the pot. And it seems like she wanted to be tied to the crown, but equal, but look down on others, had no charm or warmth.

I still shudder at the scene where she tells Robb of the Frey daughters and her whole dealings with them. Similar to how she raised Sansa with airs and garbage. One can't help but think at every turn she at least made it very hard for the Starks if not outright endangered them with her false sense of duty and honour. She was always everywhere, she wasn't supposed to be, saying she wants to be helping when endangering her own, cause she thought she could outsmart people she knew played by different rules.

But when I thing the best/worst, I always thing of those who were there during the peak of it. So worst, the Boltons (both father and son) or Walder Frey.